No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Inborn Errors of Metabolism Involving Complex Molecules: Lysosomal and Peroxisomal Storage Diseases
Abstract
Peroxisomes and lysosomes are distinct subcellular compartments that underlie several pediatric metabolic disorders. Knowledge of their function and cell biology leads to understanding how the disorders result from genetic defects. Diagnostic and therapeutic approaches for the disorders take advantage of the cell biology mechanisms. Whereas peroxisomal disorders are characterized by enzymatic defects in peroxisomal pathways leading to metabolic and lipid changes, lysosomal storage disorders are marked by accumulation of substrates of lysosomal pathways inside the lysosome. The human diseases related to these two organelles are reviewed, focusing on general disease patterns and underlying diagnosis and treatment principles.
... Peroxisomes and lysosomes are cellular organelles that perform distinct metabolic functions. Impairment in these organelles can lead to several metabolic disorders (66). Peroxisomal disorders presenting with seizures include Zellweger spectrum disorder and X-linked adrenoleukodystrophy. Lysosomal disorders presenting with seizures include Gaucher disease type 2 and 3, Niemann-Pick type C, metachromatic leukodystrophy, neuronal ceroid lipofuscinosis, sialidosis, and GM1 and GM2 gangliosidosis ( Table 1). ...
... They are also involved in the synthesis of several substrates including bile acids and plasmalogens. Defects in peroxisomal biogenesis result in Zellweger spectrum disorder which is an autosomal recessive disease with an estimated prevalence of 1:50,000 (66,67). ...
... The adolescent and adult presentations typically include dementia or psychiatric manifestations. The diagnosis is confirmed molecularly by identifying mutations in NPC1 or NPC2 genes and management is symptomatic (66,70). ...
Metabolic diseases should always be considered when evaluating children presenting with seizures. This is because many metabolic disorders are potentially treatable and seizure control can be achieved when these diseases are appropriately treated. Seizures caused by underlying metabolic diseases (metabolic seizures) should be particularly considered in unexplained neonatal seizures, refractory seizures, seizures related to fasting or food intake, seizures associated with other systemic or neurologic features, parental consanguinity, and family history of epilepsy. Metabolic seizures can be caused by various amino acids metabolic disorders, disorders of energy metabolism, cofactor-related metabolic diseases, purine and pyrimidine metabolic diseases, congenital disorders of glycosylation, and lysosomal and peroxisomal disorders. Diagnosing metabolic seizures without delay is essential because the immediate initiation of appropriate therapy for many metabolic diseases can prevent or minimize complications.
... This group comprises probably the best recognized/defined IEMs, the lysosomal storage disorders (LSD), as well as rarer large molecule metabolism disorder eg, glycogenosis and neural lipid storage disorders. 25,34 As with their small molecule counterparts, they are generally devoid of antenatal manifestations but can present with progressive neurodegeneration during childhood or adult life, alongside variable "storage signs" eg, hepatomegaly, and other disease specific multi-organ involvement. As with small molecule "accumulation" defects, some are (at least partially) treatable. ...
... The majority of mucopoysaccharidoses(MPS) have neurological involvement as a core feature. 34 Dystonia, typically generalized with prominent facial/oromandibular involvement (sometimes producing characteristic "grimacing") is the most typical MD, though ataxia and parkinsonism can also be seen. 50 Hepatomegaly is a core disease feature, though despite its large size, hepatic dysfunction is not universal. ...
The association of movement disorders with structural or functional hepatic disease occurs in three principal scenarios: a) combined involvement of both organ systems from a single disease entity, b) nervous system dysfunction resulting from exposure to toxic compounds in the setting of defective hepatic clearance, or c) hepatic or neurological injury secondary to exposure to exogenous drugs or toxins. An important early step in the workup of any patient with combined movement disorders and liver disease is the exclusion of Wilson's disease. Diagnostic delay remains common for this treatable disorder, and this has major implications for patient outcomes. Thereafter, a structured approach integrating variables such as age of onset, tempo of progression, nature and severity of liver involvement, movement disorder phenomenology, exposure to drugs/toxins and laboratory/neuroimaging findings is key to ensuring timely diagnosis and disease‐specific therapy. Herein, we provide an overview of disorders which may manifest with a combination of movement disorders and liver disease, structured under the three headings as detailed above. In each section, the most common disorders are discussed, along with important clinical pearls, suggested diagnostic workup, differential diagnoses and where appropriate, treatment considerations. This article is protected by copyright. All rights reserved.
... Lysosomal storage disorders (LSDs) are a group of about 70 inherited metabolic diseases [1] caused by deficiencies in lysosomal acid hydrolases, membrane proteins or transporters. This results in abnormal accumulation of undegraded macromolecules within the endolysosomal system and dysregulation of this pathway [2]. Although many LSDs had already been recognized as clinical entities since the 19th century, their classification started many years later with the discovery of the lysosome by Christian de Duve in 1955 [3] and with the establishment of the concept of lysosomal diseases by Hers in 1965 [4]. ...
... As in human pathology, dGBA1b mutant and dGBA1a,b double mutant showed lack of enzyme activity and significant accumulation of glycosylceramide in their heads [116,119], with subsequent increase in lysosomes number and size, which leads to a dysregulation of autophagy and the further accumulation of undegraded poly-ubiquitinated protein in whole flies and in heads [117,[119][120][121]. The dysregulation of autophagy, whose accumulation of Ref (2)p is a marker [117], also leads to the accumulation of giant and dysfunctional mitochondria and a subsequent hypersensitivity to oxidative stress. Elevation in levels of Hsc70-3 (Heat shock 70-kDa protein cognate 3, orthologue for mammalian BiP, endoplasmic reticulum chaperone BiP) mRNA, Xbp1 (X-box binding protein 1) splicing and in the level of phosphorylated eIF2α (eukaryotic translation initiation factor 2α) in mutated flies are markers of activation of Unfolded Protein Response pathway and of stress of endoplasmic reticulum [118,119,122]. ...
Lysosomal storage disorders (LSDs) represent a complex and heterogeneous group of rare genetic diseases due to mutations in genes coding for lysosomal enzymes, membrane proteins or transporters. This leads to the accumulation of undegraded materials within lysosomes and a broad range of severe clinical features, often including the impairment of central nervous system (CNS). When available, enzyme replacement therapy slows the disease progression although it is not curative; also, most recombinant enzymes cannot cross the blood-brain barrier, leaving the CNS untreated. The inefficient degradative capability of the lysosomes has a negative impact on the flux through the endolysosomal and autophagic pathways; therefore, dysregulation of these pathways is increasingly emerging as a relevant disease mechanism in LSDs. In the last twenty years, different LSD Drosophila models have been generated, mainly for diseases presenting with neurological involvement. The fruit fly provides a large selection of tools to investigate lysosomes, autophagy and endocytic pathways in vivo, as well as to analyse neuronal and glial cells. The possibility to use Drosophila in drug repurposing and discovery makes it an attractive model for LSDs lacking effective therapies. Here, ee describe the major cellular pathways implicated in LSDs pathogenesis, the approaches available for their study and the Drosophila models developed for these diseases. Finally, we highlight a possible use of LSDs Drosophila models for drug screening studies.
... In the antenatal period, true irreversible major malformations due to IEMs can be found in O-glycosylation disorder; in cholesterol synthesis defects, in amino acid synthesis disorders (glutamine and asparagine) and in mitochondrial disorders (8,9). ...
... Finally, IEMs involved with complex molecules such as peroxisomal diseases are associated with dysmorphologies, seizures, severe hypotonia and cholestatic liver disease while lysosomal disorders represent a group that involve abnormal accumulation of metabolites in various organs and tissues resulting in multi-system dysfunction: dwarfism, hepatosplenomegaly, recurrent infections, skeletal dysplasias and neurocognitive impairment (8). ...
Inborn errors of metabolism (IEMs) are rare genetic or inherited disorders resulting from an enzyme defect in biochemical and metabolic pathways affecting proteins, fats, carbohydrates metabolism or impaired organelle function presenting as complicated medical conditions involving several human organ systems. They involve great complexity of the underlying pathophysiology, biochemical workup, and molecular analysis, and have complicated therapeutic options for management. Age of presentation can vary from infancy to adolescence with the more severe forms appearing in early childhood accompanied by significant morbidity and mortality. The understanding of these complex disorders requires special in-depth training, American Board of Medical Genetics and Genomics (ABMGG) certification and experience. Most primary care physicians (PCPs) are reluctant to deal with IEM due to unfamiliarity and rarity of such conditions compounded by prompt progression to crisis situations along with paucity of time involved in dealing with such complex disorders. While there are biochemical geneticists aka metabolic specialists' expertise available, mostly in larger academic medical centers, with expertise to deal with these rare complex issues, their initial clinical presentation in most newborns, children, adolescents or adults including asymptomatic positive newborn screen (NBS), occur in the out-patient PCP settings. Therefore, it is important that PCPs' comfort to recognize early signs and symptoms is important to initiate appropriate diagnostic and therapeutic interventions, and be able to make appropriate referrals. The following article reviews common IEM clinical presentations for a robust diagnostic differential and discuss evaluation and management approaches of patients with known or suspected IEM.
... Dementia and mental retardation are the common clinical symptoms of lipid storage diseases (Rohrbach & Clarke, 2007). Inborn error of metabolism involving lysosomes is shown in Fig. 3 (Bellettato, Hubert, Scarpa, & Wangler, 2018). Metabolites are exported from lysosomes through transport protiens within transport membrane. ...
Human body encounters thousands of chemicals in the form of drugs, food items, toxins, and other environmental pollutants. These agents are treated with the help of biomolecules called enzymes or more specific drug-metabolizing enzymes (DMEs). These exogenous substances have to pass certain chemical steps in order to become active, inactive, less toxic, more toxic, or easy to excrete out of body compartments after their biological actions. DMEs decide when, where, and for how long a given substance will pose its effects endogenously. Metabolism of drugs (xenobiotics) is always a core issue of bioscience research for its importance in fate of a chemical substance inside the body. The marked problems with these enzymes are certain disorders and agents enhancing or alleviating their biological roles termed as enzymes inducers and enzymes inhibitors, respectively. Such disorders mostly affecting the role of DMEs are those of major organs such as liver, kidneys, and gastrointestinal tract where DMEs are predominantly housed. Information provided in this chapter will help healthcare professionals to carry out dose adjustment, therapeutic drug monitoring, and prescription modification better than before. This will improve the treatment outcomes of a number of therapies related to in vivo enzymatic actions. The major chronic and acute diseases interfering with the functions of enzymes involving drug metabolism and the challenges and strategies about the fate of these enzymes involving drug metabolism have been discussed in this chapter.
... Lysosomal storage diseases (LSDs) encompass more than 70 inherited diseases, which occur during infancy and childhood (1:5000 newborns), mainly characterized by a progressive neurodegenerative clinical course [94]. Despite the fact that the pathogenesis is still not currently well understood, the main mechanism causing the disease is the accumulation of metabolic substrates within lysosomes or peroxisomes, due to genetic de-fects in lysosomal enzymes or lysosomal membrane proteins [95][96][97]. Lysosomal dysfunction affects, basically, all body tissues, although its serious effects mainly concern the central nervous system, meaning that affected patients display progressive psycho-neurological impairments, accompanied by a broad spectrum of other clinical phenotypes, such as seizures, facial and other bone deformities, problems with vision and hearing, difficulty breathing, anemia and an enlarged spleen or liver [98,99]. For many LSDs, there are approved disease-specific therapies based on enzyme replacement (ERT) [100][101][102], or on intravenous administration of recombinant proteins [103][104][105], accompanied by treatment of the neurological complications, such as anticonvulsant medication, ventilatory support, assistance for patients with learning disability, orthopedic interventions and nutritional support [106,107]. ...
Metabolic disorders are very common in the population worldwide and are among the diseases with the highest health utilization and costs per person. Despite the ongoing efforts to develop new treatments, currently, for many of these disorders, there are no approved therapies, resulting in a huge economic hit and tension for society. In this review, we recapitulate the recent advancements in stem cell (gene) therapy as potential tools for the long-term treatment of both inherited (lysosomal storage diseases) and acquired (diabetes mellitus, obesity) metabolic disorders, focusing on the main promising results observed in human patients and discussing the critical hurdles preventing the definitive jump of this approach from the bench to the clinic.
... The mucopolysaccharidoses (MPS) are diseases caused by disturbances in glycosaminoglycans' (GAGs) degradation . These enzyme defects lead to severe and multisystemic effects and characteristic clinical symptoms [2][3][4]. The MPS types are classified according to the affected gene. ...
Mucopolysaccharidoses (MPS) are lysosomal storage diseases (LSDs) caused by the deficiency of enzymes essential for the metabolism of extracellular matrix components called glycosaminoglycans (GAGs). To understand the physiopathology and alterations due to the lysosomal accumulation resulting from enzymatic deficiencies and their secondary outcomes can improve the diagnosis and treatment of rare genetic diseases. This work presents a database for differentially expressed genes from different public MPS data. We developed our database, including 13 studies previously deposited in the GEO (https://www.ncbi.nlm.nih.gov/geo/). The website is hosted in the UFRGS data processing center (CPD) and is available at <https://www.ufrgs.br/mpsbase/>. The site was constructed in PHP, and the analyses were performed in R. The organisms represented by the datasets are Canis lupus familiaris, Homo sapiens, Mus musculus, and Rattus norvegicus. The user can search for the differentially expressed genes and ontologies by species, MPS type, or tissue type. For each comparison, a heatmap with the 50 top differentially expressed genes is available as well as dot plots for the 30 top ontologies divided by biological process, cellular component, KEGG pathways, and molecular function. This data is also fully available in tables. There are 54 possible comparisons involving about 5000 to 10,000 genes each. This website is the only specific database for MPS with filtering and presenting their results in a one-click approach to the best of our knowledge. The development of such analytical and automated strategies accessible to health professionals is essential for fostering MPS research. The MPSBase is a web user-friendly, comprehensive repository of differentially expressed genes and ontologies regarding the MPS data.
... A paper review lysosomal storage disease [51]. A couple of 2018 papers that had dealt with reviews of the issue [52,53] did not deal with analytical procedures; nor did those that had dealt with decisions to implement such detection methods [54,55] or those that had dealt with the follow up and management of detected cases [56,57]. Those that had studied biomarkers [57,58] and the consensus guidelines for neonatal screening, diagnosis, and treatment [59,60] as well as those that had studied costs [61] did not consider the possibility of using what has been exposed, which should improve what has been done so far, on a few diseases. ...
Few current methods are efficient to detect a high number of lysosomal storage disorders (LSDs) in newborn screening. Therefore, we propose a stepwise procedure that starts with the use of paper borne urine samples (Berry-Woolf specimen) for the inexpensive detection of elevated lysosomal content and the identification of which of the three majors biochemical groups-mucopolysaccharides, oligosaccharides, and glycosphingolipids-is detected. Urine samples are preferable to blood samples because of their higher concentrations of the relevant analytes. Subsequent steps would precisely determine which enzyme deficiency is involved. As a summary, following our previous papers on the detection of elevated oligosaccharides and mucopolysaccharides, here we describe how elevated urinary glycosphingolipids (GSLs) could be fluorometrically detected using the reagent 5-hydroxy-1-tetralone (HOT) and subsequently identified with precision by continuous thin layer chromatography or other techniques. We also outline the steps required for the validation of this procedure for its introduction in newborn screening programs.
... In general, sphingolipidoses have an incidence of approximately 1 in 10,000 individuals. Although this represents a low incidence in most populations, certain populations, especially those that are relatively isolated either geographically or culturally, have a substantially higher incidence [14,15]. Such disorders cause critical membrane impairment, and hence affect the survival and growth of most cells, especially neural cells. ...
Johann Ludwig Wilhelm Thudicum described sphingolipids (SLs) in the late nineteenth century, but it was only in the past fifty years that SL research surged in importance and applicability. Currently, sphingolipids and their metabolism are hotly debated topics in various biochemical fields. Similar to other macromolecular reactions, SL metabolism has important implications in health and disease in most cells. A plethora of SL-related genetic ailments has been described. Defects in SL catabolism can cause the accumulation of SLs, leading to many types of lysosomal storage diseases (LSDs) collectively called sphingolipidoses. These diseases mainly impact the neuronal and immune systems, but other systems can be affected as well. This review aims to present a comprehensive, up-to-date picture of the rapidly growing field of sphingolipid LSDs, their etiology, pathology, and potential therapeutic strategies. We first describe LSDs biochemically and briefly discuss their catabolism, followed by general aspects of the major diseases such as Gaucher, Krabbe, Fabry, and Farber among others. We conclude with an overview of the available and potential future therapies for many of the diseases. We strive to present the most important and recent findings from basic research and clinical applications, and to provide a valuable source for understanding these disorders.
... In the differentials of this case, inborn errors of metabolism possess importance and clinical features suggest that patients might have glycogen storage disorders (GSDs) or lysosomal storage diseases (LSDs) [22,23]. Although arterial blood gases, serum lactate, ammonia, and blood sugar were in their normal limits, we could not evaluate the characteristic enzyme levels specific for GSDs and LSDs due to financial constraints. ...
Chronic liver disease (CLD) presents as jaundice and abdominal distention. It has significant morbidity and mortality. CLD is often
associated with cirrhosis of the liver and causes of CLD vary from infection to metabolic diseases. Here we present a case of a
7-year-old female who presented with abdominal distention and shortness of breath. Her liver function tests were not normal. An
enlarged liver was found on ultrasound and computed tomography scan showed moderate ascites with heterogeneous nodular
enhancement on the liver surface. Workup for Wilson disease, viral infections, and autoimmune causes was found to be negative.
There was no evidence of metabolic diseases. Biopsy of the liver showed evidence of cirrhosis. No evidence of esophageal varices
was found. Supportive management for CLD was started. The case highlights the importance of detailed workup for identification of
the cause which can be difficult in a resource-limited setting.
This expert-opinion-based document was prepared by a group of specialists in pediatric inherited metabolic diseases and infectious diseases including administrative board members of Turkish Society for Pediatric Nutrition and Metabolism to provide guidance for the care of children with lysosomal storage disorders (LSDs) during the COVID-19 pandemic in Turkey. The experts reached consensus on key areas of focus regarding COVID-19-based risk status in relation to intersecting immune-inflammatory mechanisms and disease patterns in children with LSDs, diagnostic virus testing, particularly preventive measures and priorities during the pandemic, routine screening and diagnostic interventions for LSDs, psychological and socioeconomic impact of confinement measures and quarantines and optimal practice patterns in managing LSDs and/or COVID-19. The participating experts agreed on the intersecting characteristics of immune-inflammatory mechanisms, end-organ damage and prognostic biomarkers in LSD and COVID-19 populations, emphasizing the likelihood of enhanced clinical care when their interaction is clarified via further studies addressing certain aspects related to immunity, lysosomal dysfunction and disease pathogenesis. In the context of the current global COVID-19 pandemic, this expert-opinion-based document provides guidance for the care of children with LSDs during the COVID-19 pandemic based on the recent experience in Turkey.
There is an increasing demand for high-standard fetal and infant neuropathology examinations. Novel imaging techniques, development of new diagnostic methods and advances in genetics have stimulated the interest in gaining additional knowledge on developmental, perinatal and neonatal neuropathology. Approaching the subject from a practical standpoint, diagnostic templates for reports are provided in this essential guide to aid clinicians with different areas of expertise. Each chapter will includes numerous high-quality images, accompanied by explanatory legends from the authors' own experiences. Covering autopsy and tissue processing techniques, the authors discuss a range of disorders such as neural tube defects, brain tumours, storage disorders and many others. This book provides access to an online version on Cambridge Core, which can be accessed via the code printed on the inside of the cover. Compiling the latest advances in fetal and infant diagnostics and care, this book is a highly valuable educational resource.
There is an increasing demand for high-standard fetal and infant neuropathology examinations. Novel imaging techniques, development of new diagnostic methods and advances in genetics have stimulated the interest in gaining additional knowledge on developmental, perinatal and neonatal neuropathology. Approaching the subject from a practical standpoint, diagnostic templates for reports are provided in this essential guide to aid clinicians with different areas of expertise. Each chapter will includes numerous high-quality images, accompanied by explanatory legends from the authors' own experiences. Covering autopsy and tissue processing techniques, the authors discuss a range of disorders such as neural tube defects, brain tumours, storage disorders and many others. This book provides access to an online version on Cambridge Core, which can be accessed via the code printed on the inside of the cover. Compiling the latest advances in fetal and infant diagnostics and care, this book is a highly valuable educational resource.
The number of gene therapies in clinical trials and moving toward licensure is increasing. Most gene therapies are designed to achieve long-term effects, but at licensure the data to support claims of long-term durability are often limited, as long-term monitoring studies are often part of post-approval commitments by companies. Health technology assessors must therefore assess the potential for the long-term durability of a product and the potential cost–effectiveness based on the data available. The authors explored the benefit of strengthening the ability to infer durability of effect using analogue category data. Different analogue categories were assessed for the potential to substantiate claims of sustainability of effect for gene therapies by leveraging biological plausibility arguments. The authors propose a pathway for identifying potential analogues. Such a pathway should help establish plausible or theoretical long-term outcomes that can be considered in value assessments of gene therapies.
Background & aims:
Lysosomal storage disorders (LSDs) remain a significant cause of morbidity in the Indian population and treatment is largely out of reach for most patients. Although data on enzymatic and molecular diagnosis of Gaucher disease (GD) and Fabry disease (FD) in Indian patients are available, the present study intended to establish the pathogenic levels of Lyso GL-1 and Lyso GL-3 in patients of GD and FD respectively as diagnostic aids.
Materials and methods:
From 2017-2019, ninety confirmed Gaucher cases (by enzymatic and molecular analysis) were tested for chitotriosidase (fluorometrically) and Lyso GL-1 (LC-MS/MS) and ten confirmed Fabry cases were analyzed for Lyso GL-3 (LC-MS/MS) Results: Lyso GL-1 (median: 685.5 ng/mL, cut-off: 14) and Lyso GL-3 (median: 75.6 ng/mL, cut-off: 3.5) were found to be elevated in all enzymatically deficient patients of GD and FD respectively, however, no specific trend was observed between the levels of these biomarkers and the pathogenic variant(s) present in the patients of these disorders.
Conclusions:
This is the first report on Lyso GL-1 and Lyso GL-3 levels in Indian patients of GD and FD respectively. These results will be useful for early diagnosis to improve management of these LSDs.
inherited immunohematological and metabolic diseases have the potential to improve significantly, or be cured, using haematopoietic stem cell transplantation (HSPC) gene therapy Until autologous HSPC gene therapy makes it to the clinic, a lot of financial and logistical issues must be resolved. Conventional methods make use of centralized production facilities and a small number of specialist treatment facilities for sickness and gene therapy, but totally automated transduction may make this paradigm obsolete. The use of alkylating medications for conditioning is connected to both short-and long-term negative outcomes. The adoption of antibody-based conditioning regimens that target molecules expressed on host haematopoietic cells, such as CD117 or CD45, might allow for a decrease in alkylating agent dosage.Preclinical research has suggested that direct intravascular distribution of viral vectors would be a good alternative to ex vivo gene transfer, however with limited efficacy. A therapeutic impact and unwanted transgenic-related damage is occasionally sought. Locus-specific gene editing may be able to make use of naturally occurring gene control mechanisms. On the other hand, synthetic minigenes may not always reproduce gene expression in cells and may require complicated design. The improved efficiency in gene editing will almost probably lead to an increase in the number of therapeutic applications for gene-edited HSPCs. Although gene editing is theoretically safer than vector-based gene addition approaches, the clinical safety of HSPC gene therapy has yet to be proved. Double-strand breaks can create rearrangements such as deletions, inversions, and translocations, but Cas9 nucleases might suppress any residual issues. Base editing and prime editing can increase genome engineering safety and efficiency. In gene therapy, much further development is necessary before gene editing may be applied in a clinical-scale setting. Clinical translation of complex cellular therapies is aided by previous advances in vector-based gene therapy, which has opened the way for the area of genome editing. A gene editing evaluation needs alterations in tests and methodologies.Most HSPC gene therapies have been utilized to address specific genetic diseases. The longevity and safety of HSPC gene therapy may increase, thereby presenting the possibility of addressing new illness conditions. Consider the scenario of treatment that may last for a long time if HSPC-derived microglia was utilized. Biological systemic treatment delivery and/or elimination of blood disease reservoirs might potentially enhance chronic infectious diseases and cancer. The chimeric antigen receptors of T cells, for example, can cure several forms of haematological cancers. HSPC gene therapy will increase greatly in the future, addressing a larger spectrum of immune haematological and neurometabolic disorders.
Haematopoietic stem and progenitor cell (HSPC) gene therapy has emerged as an effective treatment modality for monogenic disorders of the blood system such as primary immunodeficiencies and β-thalassaemia. Medicinal products based on autologous HSPCs corrected using lentiviral and gammaretroviral vectors have now been approved for clinical use, and the site-specific genome modification of HSPCs using gene editing techniques such as CRISPR–Cas9 has shown great clinical promise. Preclinical studies have shown engineered HSPCs could also be used to cross-correct non-haematopoietic cells in neurodegenerative metabolic diseases. Here, we review the most recent advances in HSPC gene therapy and discuss emerging strategies for using HSPC gene therapy for a range of diseases.
Eukaryotic cells achieved a high level of organizational complexity by restricting biochemical reactions into membrane-bound organelles. Recent breakthroughs have revealed close physical connections between cellular organelles. These inter-organelle membrane contact sites are held together by specialized tethering proteins, and function to enable rapid and efficient transfer of lipids, ions and other metabolites between compartments. Defects in membrane contact sites have been implicated in Alzheimer’s disease, cancer, diabetes and other metabolic disorders highlighting their critical role in cellular homeostasis. This review summarizes the major discoveries and discusses the structural and functional diversity of membrane contact sites.
The direct and indirect effects of Coronavirus Disease-19 (COVID-19) pandemic, on Italian patients with lysosomal storage disorders receiving therapy, were analyzed by a phone questionnaire. No proved COVID-19 emerged among 102 interviewed. No problems were reported by patients receiving oral treatments. Forty-nine% of patients receiving enzyme replacement therapy in hospitals experienced disruptions, versus 6% of those home-treated. The main reasons of missed infusions were fear of infection (62.9%) and re-organization of the infusion centers (37%).
Objective
To describe the health status of young patients affected by inborn errors of metabolism that require adherence to a restricted diet (IEMRDs) and to describe and compare their self- and proxy (parent)-reported quality of life (QoL) with reference values.
Study design
A cross-sectional study was conducted in 2015-2017 in patients affected by IEMRDs (except phenylketonuria) younger than 18 years. Data collection was based on medical records, clinical examinations, parents' and children's interviews, and self-reported questionnaires. Measurements included clinical and healthcare data, child and family environment data, and self- and proxy (parent)-reported QoL.
Results
Of the 633 eligible participants, 578 were recruited (50.3% boys; mean age: 8.7 years); their anthropometric status did not differ from the general population. Approximately one-half of them had at least 1 complication of the disease. Their self-reported global QoL did not differ from that of the general population. However, relations with friends and leisure activities QoL domains were negatively impacted, whereas relations with medical staff, relations with parents, and self-esteem QoL domains were positively impacted. Their proxy (parent)-reported QoL was negatively impacted.
Conclusions
Young patients affected by IEMRDs present a high rate of clinical complications. Although their proxy (parent)-reported QoL was negatively impacted, their self-reported QoL was variably impacted (both positively and negatively). These results may inform counseling for those who care for affected patients and their families.
Sarcopenia and osteopenia/osteoporosis are two frequent conditions that often coexist amongst frail, older adults. Individuals affected from both conditions at the same time harbor a risk for adverse outcome that is substantially higher than the additive risk related to each of the two diseases. This observation lead to the description of a new entity called osteosarcopenia. Affected patients benefit from an appropriate care plan, which is based on a correct diagnosis. Establishment of the diagnosis includes the assessment of clinical risk factors and the determination of bone and muscle mass. The latter two are measured by dual-energy X-ray absorptiometry (DXA). Additional aspects in the workup of patients with osteosarcopenia include the biochemical assessment of bone and muscle metabolism and the exploration of secondary causes, such as hyperparathyroidism, vitamin D deficiency or malnutrition. Considering that these conditions can potentially be treated, patients benefit substantially from early diagnosis and treatment. Guidelines that provide specific recommendations for biochemical tests during the workup of osteosarcopenic patients are currently lacking. Therefore, the following pages provide a rather subjective overview based on the practical experience of the authors and existing separate guidelines for osteoporosis and sarcopenia. Furthermore, histomorphometric analyses and genetic tests will be addressed.
Aim:
To evaluate the results of prenatal enzymatic diagnostic studies for detecting lysosomal storage diseases (LSDs) during 1992-2018.
Methods:
Pregnancies subjected to "prenatal enzymatic diagnosis of LSDs" during 1992-2018 were retrospectively evaluated in terms of invasive prenatal tests, type of LSDs and obstetric outcomes.
Results:
A total of 142 pregnancies were evaluated for various types of LSDs of which 30, 103, and 9 cases were subjected to amniocentesis, chorionic villus sampling, and fetal blood sampling, respectively. Retrospective analysis of prenatal diagnosis revealed that LSDs affected 33% (47/142) of the fetuses. Neurologic findings were observed at the age of 1 and death occured at the age of 2 Sandhoff disease (28%), Tay-Sachs disease (27%), and Metachromatic leukodystrophy (MLD) (20%) were the most frequent LSDs among the evaluated cases with two false negatives, one each for Tay-Sachs disease and MLD.
Conclusion:
Enzymatic prenatal diagnoses of certain LSDs may serve as a primary intervention point for families with index cases of infantile or late infantile types of LSDs, since they are associated with poor outcomes, including mortality. In addition, enzyme studies alone may also be feasible for populations with increased risk of molecular heterogeneity, novel mutations, and low-income settings where genetic analysis is inaccessible.
Background:
Fabry disease is an X-linked lysosomal storage disorder caused by GLA mutations, resulting in α-galactosidase (α-Gal) deficiency and accumulation of lysosomal substrates. Migalastat, an oral pharmacological chaperone being developed as an alternative to intravenous enzyme replacement therapy (ERT), stabilises specific mutant (amenable) forms of α-Gal to facilitate normal lysosomal trafficking.
Methods:
The main objective of the 18-month, randomised, active-controlled ATTRACT study was to assess the effects of migalastat on renal function in patients with Fabry disease previously treated with ERT. Effects on heart, disease substrate, patient-reported outcomes (PROs) and safety were also assessed.
Results:
Fifty-seven adults (56% female) receiving ERT (88% had multiorgan disease) were randomised (1.5:1), based on a preliminary cell-based assay of responsiveness to migalastat, to receive 18 months open-label migalastat or remain on ERT. Four patients had non-amenable mutant forms of α-Gal based on the validated cell-based assay conducted after treatment initiation and were excluded from primary efficacy analyses only. Migalastat and ERT had similar effects on renal function. Left ventricular mass index decreased significantly with migalastat treatment (-6.6 g/m(2) (-11.0 to -2.2)); there was no significant change with ERT. Predefined renal, cardiac or cerebrovascular events occurred in 29% and 44% of patients in the migalastat and ERT groups, respectively. Plasma globotriaosylsphingosine remained low and stable following the switch from ERT to migalastat. PROs were comparable between groups. Migalastat was generally safe and well tolerated.
Conclusions:
Migalastat offers promise as a first-in-class oral monotherapy alternative treatment to intravenous ERT for patients with Fabry disease and amenable mutations.
Trial registration number:
NCT00925301; Pre-results.
Peroxisomal biogenesis disorders (PBD) are caused by mutations in PEX genes, and are typically diagnosed with biochemical testing in plasma followed by confirmatory testing. Here we report the unusual diagnostic path of a child homozygous for PEX1 p.G843D. The patient presented with sensorineural hearing loss, pigmentary retinopathy, and normal intellect. After testing for Usher syndrome was negative, he was found to have PBD through a research sequencing panel. When evaluating a patient with hearing loss and pigmentary retinopathy, mild PBD should be on the differential regardless of cognitive function.
Missense mutations in the lysosomal hydrolase β‐galactocerebrosidase (GALC) account for at least 40% of known cases of Krabbe disease (KD). Most of these missense mutations are predicted to disrupt the fold of the enzyme, preventing GALC in sufficient amounts from reaching its site of action in the lysosome. The predominant central nervous system (CNS) pathology and the absence of accumulated primary substrate within the lysosome mean that strategies used to treat other lysosomal storage disorders (LSDs) are insufficient in KD, highlighting the still unmet clinical requirement for successful KD therapeutics. Pharmacological chaperone therapy (PCT) is one strategy being explored to overcome defects in GALC caused by missense mutations. In recent studies, several small‐molecule inhibitors have been identified as promising chaperone candidates for GALC. This Review discusses new insights gained from these studies and highlights the importance of characterizing both the chaperone interaction and the underlying mutation to define properly a responsive population and to improve the translation of existing lead molecules into successful KD therapeutics. We also highlight the importance of using multiple complementary methods to monitor PCT effectiveness. Finally, we explore the exciting potential of using combination therapy to ameliorate disease through the use of PCT with existing therapies or with more generalized therapeutics, such as proteasomal inhibition, that have been shown to have synergistic effects in other LSDs. This, alongside advances in CNS delivery of recombinant enzyme and targeted rational drug design, provides a promising outlook for the development of KD therapeutics. © 2016 The Authors. Journal of Neuroscience Research Published by Wiley Periodicals, Inc.
Adenylosuccinate lyase (ADSL) deficiency is a rare autosomal recessive neurometabolic disorder that presents with a broad-spectrum of neurological and physiological symptoms. The ADSL gene produces an enzyme with binary molecular roles in de novo purine synthesis and purine nucleotide recycling. The biochemical phenotype of ADSL deficiency, accumulation of SAICAr and succinyladenosine (S-Ado) in biofluids of affected individuals, serves as the traditional target for diagnosis with targeted quantitative urine purine analysis employed as the predominate method of detection. In this study, we report the diagnosis of ADSL deficiency using an alternative method, untargeted metabolomic profiling, an analytical scheme capable of generating semi-quantitative z-score values for over 1000 unique compounds in a single analysis of a specimen. Using this method to analyze plasma, we diagnosed ADSL deficiency in four patients and confirmed these findings with targeted quantitative biochemical analysis and molecular genetic testing. ADSL deficiency is part of a large a group of neurometabolic disorders, with a wide range of severity and sharing a broad differential diagnosis. This phenotypic similarity among these many inborn errors of metabolism (IEMs) has classically stood as a hurdle in their initial diagnosis and subsequent treatment. The findings presented here demonstrate the clinical utility of metabolomic profiling in the diagnosis of ADSL deficiency and highlights the potential of this technology in the diagnostic evaluation of individuals with neurologic phenotypes.
Introduction:
Zellweger spectrum disorders (ZSDs) are characterized by a failure in peroxisome formation, caused by autosomal recessive mutations in different PEX genes. At least some of the progressive and irreversible clinical abnormalities in patients with a ZSD, particularly liver dysfunction, are likely caused by the accumulation of toxic bile acid intermediates. We investigated whether cholic acid supplementation can suppress bile acid synthesis, reduce accumulation of toxic bile acid intermediates and improve liver function in these patients.
Methods:
An open label, pretest-posttest design study was conducted including 19 patients with a ZSD. Participants were followed longitudinally during a period of 2.5 years prior to the start of the intervention. Subsequently, all patients received oral cholic acid and were followed during 9 months of treatment. Bile acids, peroxisomal metabolites, liver function and liver stiffness were measured at baseline and 4, 12 and 36 weeks after start of cholic acid treatment.
Results:
During cholic acid treatment, bile acid synthesis decreased in the majority of patients. Reduced levels of bile acid intermediates were found in plasma and excretion of bile acid intermediates in urine was diminished. In patients with advanced liver disease (n = 4), cholic acid treatment resulted in increased levels of plasma transaminases, bilirubin and cholic acid with only a minor reduction in bile acid intermediates.
Conclusions:
Oral cholic acid therapy can be used in the majority of patients with a ZSD, leading to at least partial suppression of bile acid synthesis. However, caution is needed in patients with advanced liver disease due to possible hepatotoxic effects.
Peroxisome biogenesis disorders in the Zellweger spectrum (PBD-ZSD) are a heterogeneous group of genetic disorders caused by mutations in PEX genes responsible for normal peroxisome assembly and functions. As a result of impaired peroxisomal activities, individuals with PBD-ZSD can manifest a complex spectrum of clinical phenotypes that typically result in shortened life spans. The extreme variability in disease manifestation ranging from onset of profound neurologic symptoms in newborns to progressive degenerative disease in adults presents practical challenges in disease diagnosis and medical management. Recent advances in biochemical methods for newborn screening and genetic testing have provided unprecedented opportunities for identifying patients at the earliest possible time and defining the molecular bases for their diseases. Here, we provide an overview of current clinical approaches for the diagnosis of PBD-ZSD and provide broad guidelines for the treatment of disease in its wide variety of forms. Although we anticipate future progress in the development of more effective targeted interventions, the current guidelines are meant to provide a starting point for the management of these complex conditions in the context of personalized health care.
Zellweger spectrum disorders (ZSDs) represent the major subgroup within the peroxisomal biogenesis disorders caused by defects in PEX genes. The Zellweger spectrum is a clinical and biochemical continuum which can roughly be divided into three clinical phenotypes. Patients can present in the neonatal period with severe symptoms or later in life during adolescence or adulthood with only minor features. A defect of functional peroxisomes results in several metabolic abnormalities, which in most cases can be detected in blood and urine. There is currently no curative therapy, but supportive care is available. This review focuses on the management of patients with a ZSD and provides recommendations for supportive therapeutic options for all those involved in the care for ZSD patients.
We present a patient with a unique neurological phenotype with a progressive neurodegenerative. An 18-year diagnostic odyssey for the patient ended when exome sequencing identified a homozygous PEX16 mutation suggesting an atypical peroxisomal biogenesis disorder (PBD). Interestingly, the patient's peroxisomal biochemical abnormalities were subtle, such that plasma very-long-chain fatty acids initially failed to provide a diagnosis. This case suggests that next-generation sequencing may be diagnostic in some atypical peroxisomal biogenesis disorders.
Heimler syndrome (HS) is a rare recessive disorder characterized by sensorineural hearing loss (SNHL), amelogenesis imperfecta, nail abnormalities, and occasional or late-onset retinal pigmentation. We ascertained eight families affected by HS and, by using a whole-exome sequencing approach, identified biallelic mutations in PEX1 or PEX6 in six of them. Loss-of-function mutations in both genes are known causes of a spectrum of autosomal-recessive peroxisome-biogenesis disorders (PBDs), including Zellweger syndrome. PBDs are characterized by leukodystrophy, hypotonia, SNHL, retinopathy, and skeletal, craniofacial, and liver abnormalities. We demonstrate that each HS-affected family has at least one hypomorphic allele that results in extremely mild peroxisomal dysfunction. Although individuals with HS share some subtle clinical features found in PBDs, the diagnosis was not suggested by routine blood and skin fibroblast analyses used to detect PBDs. In conclusion, our findings define HS as a mild PBD, expanding the pleiotropy of mutations in PEX1 and PEX6.
Global metabolic profiling currently achievable by untargeted mass spectrometry-based metabolomic platforms has great potential to advance our understanding of human disease states, including potential utility in the detection of novel and known inborn errors of metabolism (IEMs). There are few studies of the technical reproducibility, data analysis methods, and overall diagnostic capabilities when this technology is applied to clinical specimens for the diagnosis of IEMs. We explored the clinical utility of a metabolomic workflow capable of routinely generating semi-quantitative z-score values for ~900 unique compounds, including ~500 named human analytes, in a single analysis of human plasma. We tested the technical reproducibility of this platform and applied it to the retrospective diagnosis of 190 individual plasma samples, 120 of which were collected from patients with a confirmed IEM. Our results demonstrate high intra-assay precision and linear detection for the majority compounds tested. Individual metabolomic profiles provided excellent sensitivity and specificity for the detection of a wide range of metabolic disorders and identified novel biomarkers for some diseases. With this platform, it is possible to use one test to screen for dozens of IEMs that might otherwise require ordering multiple unique biochemical tests. However, this test may yield false negative results for certain disorders that would be detected by a more well-established quantitative test and in its current state should be considered a supplementary test. Our findings describe a novel approach to metabolomic analysis of clinical specimens and demonstrate the clinical utility of this technology for prospective screening of IEMs.
Electronic supplementary material
The online version of this article (doi:10.1007/s10545-015-9843-7) contains supplementary material, which is available to authorized users.
Gangliosides are the main glycolipids of neuronal plasma membranes. Their surface patterns are generated by coordinated processes, involving biosynthetic pathways of the secretory compartments, catabolic steps of the endolysosomal system, and intracellular trafficking. Inherited defects in ganglioside biosynthesis causing fatal neurodegenerative diseases have been described so far almost exclusively in mouse models, whereas inherited defects in ganglioside catabolism causing various clinical forms of GM1- and GM2-gangliosidoses have long been known. For digestion, gangliosides are endocytosed and reach intra-endosomal vesicles. At the level of late endosomes, they are depleted of membrane-stabilizing lipids like cholesterol and enriched with bis(monoacylglycero)phosphate (BMP). Lysosomal catabolism is catalyzed at acidic pH values by cationic sphingolipid activator proteins (SAPs), presenting lipids to their respective hydrolases, electrostatically attracted to the negatively charged surface of the luminal BMP-rich vesicles. Various inherited defects of ganglioside hydrolases, e.g., of β-galactosidase and β-hexosaminidases, and of GM2-activator protein, cause infantile (with tetraparesis, dementia, blindness) and different protracted clinical forms of GM1- and GM2-gangliosidoses. Mutations yielding proteins with small residual catabolic activities in the lysosome give rise to juvenile and adult clinical forms with a wide range of clinical symptomatology. Apart from patients' differences in their genetic background, clinical heterogeneity may be caused by rather diverse substrate specificities and functions of lysosomal hydrolases, multifunctional properties of SAPs, and the strong regulation of ganglioside catabolism by membrane lipids. Currently, there is no treatment available for neuronal ganglioside storage diseases. Therapeutic approaches in mouse models and patients with juvenile forms of gangliosidoses are discussed.
Peroxisomes are indispensable for human health and development. They represent ubiquitous subcellular organelles which compartmentalize enzymes responsible for several crucial metabolic processes such as β-oxidation of specific fatty acids, biosynthesis of ether phospholipids and metabolism of reactive oxygen species. Peroxisomes are highly flexible organelles that rapidly assemble, multiply and degrade in response to metabolic needs. Basic research on the biogenesis of peroxisomes and their metabolic functions have improved our knowledge about their crucial role in several inherited disorders and in other pathophysiological conditions. The goal of this review is to give a comprehensive overview of the role of peroxisomes in disease. Besides the genetic peroxisomal disorders in humans, the role of peroxisomes in carcinogenesis and in situations related to oxidative stress such as inflammation, ischemia-reperfusion, and diabetes will be addressed.
Lysosomal storage diseases (LSDs) are a family of disorders that result from inherited gene mutations that perturb lysosomal homeostasis. LSDs mainly stem from deficiencies in lysosomal enzymes, but also in some non-enzymatic lysosomal proteins, which lead to abnormal storage of macromolecular substrates. Valuable insights into lysosome functions have emerged from research into these diseases. In addition to primary lysosomal dysfunction, cellular pathways associated with other membrane-bound organelles are perturbed in these disorders. Through selective examples, we illustrate why the term "cellular storage disorders" may be a more appropriate description of these diseases and discuss therapies that can alleviate storage and restore normal cellular function.
In Alzheimer's disease (AD) and dementia of the Alzheimer's type (DAT), the role played by peroxisomes is not well known. Peroxisomes are present in all eukaryotic cells, with the exception of erythrocytes. They are involved in the β-oxidation process of long-chain fatty acids, very-long-chain fatty acids, and branched-chain fatty acids. They participate in the α-oxidation of phytanic acid, the biosynthesis of bile acids, and the breakdown of eicosanoids. Peroxisomes are also involved in the synthesis of specific fatty acids such as docosahexaenoic acid (DHA), which is essential for the brain and retina, and plasmalogens (PLGN), which play crucial roles in neural cells and are essential components of myelin. Several studies conducted in animal models and in humans provided evidence for a role of DHA in preventing brain degeneration. Significantly lower levels of PLGN were observed in patients with severe dementia. Moreover, a decreased activity of carnitine acetyltransferase, an enzyme present in peroxisome (but also detected in mitochondria, endoplasmic reticulum, and nucleus), was reported in AD patients. We give an overview of the potential role of peroxisomes, especially in the part played by DHA, PLGN, carnitine, and carnitine-dependent peroxisomal enzymes, on the development of AD and DAT. The potential of developing novel therapies targeted on peroxisomal metabolism to prevent cognitive decline and other age-related neurological disorders is discussed.
Fabry disease (FD) is a progressive, X-linked inherited disorder of glycosphingolipid metabolism due to deficient or absent lysosomal α-galactosidase A activity. FD is pan-ethnic and the reported annual incidence of 1 in 100,000 may underestimate the true prevalence of the disease. Classically affected hemizygous males, with no residual α-galactosidase A activity may display all the characteristic neurological (pain), cutaneous (angiokeratoma), renal (proteinuria, kidney failure), cardiovascular (cardiomyopathy, arrhythmia), cochleo-vestibular and cerebrovascular (transient ischemic attacks, strokes) signs of the disease while heterozygous females have symptoms ranging from very mild to severe. Deficient activity of lysosomal α-galactosidase A results in progressive accumulation of globotriaosylceramide within lysosomes, believed to trigger a cascade of cellular events. Demonstration of marked α-galactosidase A deficiency is the definitive method for the diagnosis of hemizygous males. Enzyme analysis may occasionnally help to detect heterozygotes but is often inconclusive due to random X-chromosomal inactivation so that molecular testing (genotyping) of females is mandatory. In childhood, other possible causes of pain such as rheumatoid arthritis and 'growing pains' must be ruled out. In adulthood, multiple sclerosis is sometimes considered. Prenatal diagnosis, available by determination of enzyme activity or DNA testing in chorionic villi or cultured amniotic cells is, for ethical reasons, only considered in male fetuses. Pre-implantation diagnosis is possible. The existence of atypical variants and the availability of a specific therapy singularly complicate genetic counseling. A disease-specific therapeutic option - enzyme replacement therapy using recombinant human α-galactosidase A - has been recently introduced and its long term outcome is currently still being investigated. Conventional management consists of pain relief with analgesic drugs, nephroprotection (angiotensin converting enzyme inhibitors and angiotensin receptors blockers) and antiarrhythmic agents, whereas dialysis or renal transplantation are available for patients experiencing end-stage renal failure. With age, progressive damage to vital organ systems develops and at some point, organs may start to fail in functioning. End-stage renal disease and life-threatening cardiovascular or cerebrovascular complications limit life-expectancy of untreated males and females with reductions of 20 and 10 years, respectively, as compared to the general population. While there is increasing evidence that long-term enzyme therapy can halt disease progression, the importance of adjunctive therapies should be emphasized and the possibility of developing an oral therapy drives research forward into active site specific chaperones.
Zellweger syndrome spectrum disorders are caused by mutations in any of at least 12 different PEX genes. This includes PEX16, which encodes an integral peroxisomal membrane protein involved in peroxisomal membrane assembly. PEX16-defective patients have been reported to have a severe clinical presentation. Fibroblasts from these patients displayed a defect in the import of peroxisomal matrix and membrane proteins, resulting in a total absence of peroxisomal remnants.
To report on six patients with an unexpected mild variant peroxisome biogenesis disorder due to mutations in the PEX16 gene. Patients presented in the preschool years with progressive spastic paraparesis and ataxia (with a characteristic pattern of progressive leucodystrophy and brain atrophy on MRI scan) and later developed cataracts and peripheral neuropathy. Surprisingly, their fibroblasts showed enlarged, import-competent peroxisomes.
Plasma analysis revealed biochemical abnormalities suggesting a peroxisomal disorder. Biochemical variables in fibroblasts were only mildly abnormal or within the normal range. Immunofluorescence microscopy revealed the presence of import-competent peroxisomes, which were increased in size but reduced in number. Subsequent sequencing of all known PEX genes revealed five novel apparent homozygous mutations in the PEX16 gene.
An unusual variant peroxisome biogenesis disorder caused by mutations in the PEX16 gene, with a relatively mild clinical phenotype and an unexpected phenotype in fibroblasts, was identified. Although PEX16 is involved in peroxisomal membrane assembly, PEX16 defects can present with enlarged import-competent peroxisomes in fibroblasts. This is important for future diagnostics of patients with a peroxisomal disorder.
In humans, peroxisomes harbor a complex set of enzymes acting on various lipophilic carboxylic acids, organized in two basic pathways, alpha-oxidation and beta-oxidation; the latter pathway can also handle omega-oxidized compounds. Some oxidation products are crucial to human health (primary bile acids and polyunsaturated FAs), whereas other substrates have to be degraded in order to avoid neuropathology at a later age (very long-chain FAs and xenobiotic phytanic acid and pristanic acid). Whereas total absence of peroxisomes is lethal, single peroxisomal protein deficiencies can present with a mild or severe phenotype and are more informative to understand the pathogenic factors. The currently known single protein deficiencies equal about one-fourth of the number of proteins involved in peroxisomal FA metabolism. The biochemical properties of these proteins are highlighted, followed by an overview of the known diseases.
The disorders of peroxisomal beta-oxidation, which have been well characterised at the molecular level, include defects of acyl-CoA oxidase, defects of the D-bifunctional protein (D-BP) (including specific defects of its enoyl-CoA hydratase and D-3-hydroxyacyl-CoA dehydrogenase components), defects of the very-long-chain fatty acid (VLCFA)-CoA importer [X-linked adrenoleukodystrophy (ALD)] and alpha-methylacyl-CoA racemase deficiency. A survey of the clinical consequences of these defects indicates that defects in the acyl-CoA oxidase and D-BP can produce neonatal hypotonia, seizures in early infancy, retinopathy and progressive neurological dysfunction with leukodystrophy on imaging. Defects in the VLCFA-CoA importer and in the racemase do not produce disease until a long time after the neonatal period. However, again the clinical picture is dominated by neurological disease: impaired cognitive function with leukodystrophy in childhood X-linked ALD and retinopathy and neuropathy in racemase deficiency. It is difficult to escape the conclusion that defective peroxisomal beta-oxidation has effects (such as impaired neuronal migration in the developing brain), which are more serious than those produced by the accumulation of substrates (VLCFAs, pristanic acid) alone.
Fabry disease is a rare X linked lysosomal storage disorder resulting from deficiency of alpha-galactosidase A activity. Although the severity of clinical features in male patients is well described, only recently have studies reported the high prevalence of disabling clinical features in heterozygous females.
This study sets out to examine the clinical features and natural history of Fabry disease in further detail in a large group of female patients.
Data were obtained from 303 females enrolled in the Fabry Outcome Survey. Pain was assessed using the Brief Pain Inventory, and health related quality of life (HRQoL) was assessed using the European Quality of Life Questionnaire. A modified version of the Mainz Severity Score Index was also applied. Data on left ventricular mass (LVM) index, mean ventricular wall thickness, and glomerular filtration rate (GFR) were used to assess cardiac and renal involvement.
The most commonly reported clinical features in females were neurological (77%) and cardiac (59%). A history of renal involvement was recorded in 40% of cases. Neurological features were the earliest to develop (mean age: 16 years), whereas cardiac (mean age: 33.5 years) and renal (mean age: 37.3 years) features developed later. LVM index increased exponentially with age. In addition, age was negatively correlated with estimated GFR and HRQoL.
Females with Fabry disease report important age related clinical features and clinical investigation demonstrates evidence of disease progression. This study highlights the importance of careful and longitudinal assessment of female heterozygote patients with Fabry disease.
D-Bifunctional protein (DBP) deficiency is an autosomal recessive disorder of peroxisomal fatty acid oxidation caused by mutations in HSD17B4. It is typically fatal by the age of two years with symptom onset during the neonatal period, and survival until late childhood is rare. We herein report the case of a patient with DBP deficiency surviving until adulthood, who showed severe sensorineural deafness, disturbances in language acquisition, slowly progressive cerebellar ataxia, and peripheral neuropathy. This patient, in whom findings of prior investigations were nondiagnostic, had been followed up as having an early-onset spinocerebellar degeneration of unknown etiology. Whole-exome sequencing analysis at the age of 36 showed two heterozygous variants in the gene HSD17B4, which encodes DBP in this patient. A panel of peroxisomal investigations showed normal levels of very long chain fatty acids (VLCFAs) in plasma and elevated serum phytanic acid levels. Recently, an increasing number of patients with DBP deficiency surviving until adolescence/adulthood have been reported, in whom abnormalities in the levels of VLCFAs and other peroxisomal metabolites are marginal or nonexistent. Genetic analysis of HSD17B4 should be considered in adult patients with cerebellar ataxia, peripheral neuropathy, and pyramidal signs in addition to sensorineural auditory disturbance since childhood.
The explosion of insights in the field of metabolic disease has shed new light on diagnostic as well as treatment options. 'Inherited Metabolic Disease-A Clinical Approach' is written with a reader-friendly consistent structure. It helps the reader to find the information in an easily accessible and rapid way when needed. Starting with an overview of the major groups of metabolic disorders it includes algorithms with questions and answers as well as numerous graphs, metabolic pathways, and an expanded index. Clinical and diagnostic details with a system and symptom based are given to facilitate an efficient and yet complete diagnostic work-up of individual patients. © Springer-Verlag Berlin Heidelberg 2010. All rights are reserved.
Patients with Zellweger Spectrum Disorders (ZSDs) have impaired peroxisome biogenesis and severe, multisystem disease. Although the neurologic symptoms of ZSD tend to be the most prominent, patients also have hepatic, renal and adrenal impairment. Little is known about bone health in patients with ZSD, particularly those with mild or moderate presentation. We investigated 13 ZSD patients who had strikingly abnormal bone mineral density for age. DXA scans showed mean lumbar and femoral neck Z-scores of -3.2. There were no major differences between ambulatory and nonambulatory patients, and no biochemical abnormalities consistent with rickets or vitamin D deficiency were seen. Cyclic bisphosphonate therapy in one ZSD patient was successfully used to increase in bone mineral density. Although the etiology of bone disease in this condition is unknown, we speculate that altered signaling through the PPARγ pathway or deficient plasmalogens in patients with ZSD disrupts osteogenesis, resulting in poor bone formation and poor mineralization. Further investigation into the pathogenic mechanisms of bone disease in ZSD and the role of peroxisomal metabolism in osteogenesis may yield insights into the pathology of bone disease and suggest novel treatment options.
Mucopolysaccharidosis and other lysosomal storage diseases are rare, chronic, and progressive inherited diseases caused by a deficit of lysosomal enzymes. Patients are affected by a wide variety of symptoms. For some lysosomal storage diseases, effective treatments to arrest disease progression, or slow the pathologic process, and increase patient life expectancy are available or being developed. Timely diagnosis is crucial. Rheumatologists, orthopedics, and neurologists are commonly consulted due to unspecific musculoskeletal signs and symptoms. Pain, stiffness, contractures of joints in absence of clinical signs of inflammation, bone pain or abnormalities, osteopenia, osteonecrosis, secondary osteoarthritis or hip dysplasia are the alerting symptoms that should induce suspicion of a lysosomal storage disease.
Peroxisomal biogenesis disorders typically cause severe multisystem disease and early death. We describe a child and an adult of normal intelligence with progressive ataxia, axonal motor neuropathy, and decreased vibration sense. Both patients had marked cerebellar atrophy. Peroxisomal studies revealed a peroxisomal biogenesis disorder. Two mutations in PEX10 were found in the child, c.992G>A (novel) and c.764_765insA, and in the adult, c.2T>C (novel) and c.790C>T. Transfection with wild-type PEX10 corrected the fibroblast phenotype. Bile acid supplements and dietary restriction of phytanic acid were started. Peroxisomal biogenesis disorders should be considered in the differential diagnosis of autosomal recessive ataxia. ANN NEUROL 2010;68:259–263
The cerebrohepatorenal syndrome of Zellweger is a congenital syndrome of multiple manifestations, including hepatomegaly and liver dysfunction. Treatment is generally of a supportive nature, aimed at improving nutrition and growth, controlling the central nervous system symptoms and limiting progression of liver disease. Because the liver disease in Zellweger syndrome may be attributed to an overproduction and accumulation of cholestanoic acids, exacerbated by diminished primary bile acid synthesis, we hypothesized that primary bile acid administration would be beneficial in improving liver function by a mechanism involving down-regulation in the synthesis of these atypical bile acids. We report here the clinical and biochemical responses to primary bile acid administration in a 2-mo-old boy who was seen with the typical signs of Zellweger syndrome. Liver disease was evident from hepatomegaly and elevated serum liver enzymes and bilirubin. The diagnosis was supported by markedly elevated serum very long chain fatty acids and the bile acids dihydroxycholestanoic acid and trihydroxycholestanoic acid. Confirmation of the lack of peroxisomes was established by electron microscopy. When the patient was 6 mo old, the primary bile acids cholic acid and chenodeoxycholic acid, (100 mg each/day) were administered orally. A significant improvement in biochemical indices of liver function occurred with a normalization of the serum bilirubin and liver enzymes and a histological improvement in the extent of inflammation and bile duct proliferation and disappearance of cannalicular plugs. Serum and urinary cholestanoic acids showed a significant decrease within a few days. A striking and sustained increase in growth was observed after therapy, and an improvement in neurological symptoms was noted. In conclusion, this study indicates that primary bile acid therapy improves liver function and growth in the patient with peroxisomal dysfunction and should be considered in the supportive therapies for this condition. (Hepatology 1992;15:198-207).
Plasmalogens are a unique class of membrane glycerophospholipids containing a fatty alcohol with a vinyl-ether bond at the sn-1 position, and enriched in polyunsaturated fatty acids at the sn-2 position of the glycerol backbone. These two features provide novel properties to these compounds. Although plasmalogens represent up to 20% of the total phospholipid mass in humans their physiological roles have been challenging to identify, and are likely to be particular to different tissues, metabolic processes and developmental stages. Their biosynthesis starts in peroxisomes, and defects at these steps cause the malformation syndrome, Rhizomelic Chondrodysplasia Punctata (RCDP). The RCDP phenotype predicts developmental roles for plasmalogens in bone, brain, lens, lung, kidney and heart. Recent studies have revealed secondary plasmalogen deficiencies associated with more common disorders and allow us to tease out additional pathways dependent on plasmalogen functions. In this review, we present current knowledge of plasmalogen biology in health and disease. This article is part of a Special Issue entitled: Metabolic Functions and Biogenesis of peroxisomes in Health and Disease.
Metachromatic leukodystrophy (MLD) represents a devastating lysosomal storage disease characterized by intralysosomal accumulation of the sphingolipid sulfatide in various tissues. Three types of the disease are currently distinguished: the late-infantile, which is the most commonly observed, the juvenile and the adult type. Demyelination represents the main histopathological feature of the disorder, leading to neurological impairment with no curative treatment currently available. Nevertheless, the increased scientific interest on the disease has led to the experimental use of innovative therapeutic approaches in animal models, aiming to provide an effective therapeutic regimen for human patients, as well. This paper provides an overview of developing treatment options among patients with MLD. Apart from hematopoietic stem cell transplantation, already in use for decades, other recent data discussed includes umbilical cord blood and stem cell transplantation, enzyme replacement therapy, gene therapy and autologous hematopoietic transplantation of genetically modified stem cells. Gene therapy with oligodedroglial, neural progenitor, embryonic and microencapsulated recombinant cells represents add-on treatment options still on experimental level.
With a constitutive recycling function and the capacity to digest exogenous material as well as endogenous organelles in the process of autophagy, lysosomes are at the heart of the living cell. Dynamic interactions with other cellular components ensure that the lysosomal compartment is a central point of convergence in countless diverse diseases. Inborn lysosomal (storage) diseases represent about 70 genetically distinct conditions, with a combined birth frequency of about 1 in 7500. Many are associated with macromolecular storage, causing physical disruption of the organelle and cognate structures; in neurons, ectopic dendritogenesis and axonal swelling due to distension with membraneous tubules and autophagic vacuoles are observed. Disordered autophagy is almost universal in lysosomal diseases but biochemical injury due to toxic metabolites such as lysosphingolipid molecules, abnormal calcium homeostasis and endoplasmic reticulum stress responses and immune-inflammatory processes occur. However, in no case have the mechanistic links between individual clinico-pathological manifestations and the underlying molecular defect been precisely defined. With access to the external fluid-phase and intracellular trafficking pathways, the lysosome and its diseases are a focus of pioneering investment in biotechnology; this has generated innovative orphan drugs and, in the case of Gaucher's disease, effective treatment for the haematological and visceral manifestations. Given that two-thirds of lysosomal diseases have potentially devastating consequences in the nervous system, future therapeutic research will require an integrative understanding of the unitary steps in their neuro pathogenesis. Informative genetic variants illustrated by patients with primary defects in this organelle offer unique insights into the central role of lysosomes in human health and disease. We provide a conspectus of inborn lysosomal diseases and their pathobiology; the cryptic evolution of events leading to irreversible changes may be dissociated from the cellular storage phenotype, as revealed by the outcome of therapeutic gene transfer undertaken at different stages of disease.
Krabbe disease (globoid cell leukodystrophy) is a neurodegenerative disorder that is caused by deficiency of the lysosomal enzyme galactosylceramidase. The resulting accumulation of incompletely metabolized galactocerebroside, which is a component of myelin, leads to progressive white matter disease. The severity of signs and symptoms is partly influenced by the causal mutations and corresponding residual enzyme activity. This review explains how the disease might manifest and discusses methods for diagnosis and staging of the disease process. The current understanding of the mechanisms underlying Krabbe disease is summarized, and therapeutic options--including current and investigational approaches--are outlined.
Peroxisome assembly disorders are genetic disorders characterized by biochemical abnormalities, including low docosahexaenoic acid (DHA). The objective was to assess whether treatment with DHA supplementation would improve biochemical abnormalities, visual function, and growth in affected individuals.
This was a randomized, double-blind, placebo-controlled trial conducted at a single center. Treatment groups received supplements of DHA (100 mg/kg per day). The primary outcome measures were the change from baseline in the visual function and physical growth during the 1 year follow-up period.
Fifty individuals were enrolled and randomized. Two were subsequently excluded from study analysis when it was determined that they had a single enzyme disorder of peroxisomal beta oxidation. Thirty-four returned for follow-up. Nine patients died during the trial of their disorder, and 5 others were lost to follow-up. DHA supplementation was well tolerated. There was no difference in the outcomes between the treated and untreated groups in biochemical function, electroretinogram, or growth. Improvements were seen in both groups in certain individuals.
DHA supplementation did not improve the visual function or growth of treated individuals with peroxisome assembly disorders. Classification of evidence: This interventional study provides Class II evidence that DHA supplementation did not improve the visual function or growth of treated individuals with peroxisome assembly disorders during an average of 1 year of follow-up in patients aged 1 to 144 months.
Metachromatic leukodystrophy (MLD) is a rare lysosomal sphingolipid storage disorder, caused by a deficiency of arylsulfatase A (ASA). It is inherited in an autosomal recessive way, among Caucasians three causing alleles are frequent. Demyelination is the hallmark of MLD. Interest in the disease has increased as therapeutic options such as stem cell transplantation, enzyme replacement and gene therapy are topics of current research. A late-infantile (onset before 3 years of age), a juvenile form (onset before 16 years) and an adult form are usually distinguished. Rapid motor decline is typical for the first and also the second forms, the second may be preceded by cognitive and behavioural problems, which mainly characterize the adult form. There is evidence for a genotype-phenotype correlation: patients homozygous for alleles which do not allow the expression of any enzyme activity (null-allele) suffer from the late infantile form; heterozygosity for a null allele and a non-null allele are more associated with the juvenile form and homozygosity for non-null alleles is more frequent in the most attenuated adult onset form.
The discovery over five decades ago of the lysosome, as a degradative organelle and its dysfunction in lysosomal storage disorder patients, was both insightful and simple in concept. Here, we review some of the history and pathophysiology of lysosomal storage disorders to show how they have impacted on our knowledge of lysosomal biology. Although a significant amount of information has been accrued on the molecular genetics and biochemistry of lysosomal storage disorders, we still do not fully understand the mechanistic link between the storage material and disease pathogenesis. However, the accumulation of undegraded substrate(s) can disrupt other lysosomal degradation processes, vesicular traffic, and lysosomal biogenesis to evoke the diverse pathophysiology that is evident in this complex set of disorders.
Although neurodegenerative diseases are most prevalent in the elderly, in rare cases, they can also affect children. Lysosomal storage diseases (LSDs) are a group of inherited metabolic neurodegenerative disorders due to deficiency of a specific protein integral to lysosomal function, such as enzymes or lysosomal components, or to errors in enzyme trafficking/targeting and defective function of nonenzymatic lysosomal proteins, all preventing the complete degradation and recycling of macromolecules. This primary metabolic event determines a cascade of secondary events, inducing LSD's pathology. The accumulation of intermediate degradation affects the function of lysosomes and other cellular organelles. Accumulation begins in infancy and progressively worsens, often affecting several organs, including the central nervous system (CNS). Affected neurons may die through apoptosis or necrosis, although neuronal loss usually does not occur before advanced stages of the disease. CNS pathology causes mental retardation, progressive neurodegeneration, and premature death. Many of these features are also found in adult neurodegenerative disorders, such as Alzheimer's, Parkinson's, and Huntington's diseases. However, the nature of the secondary events and their exact contribution to mental retardation and dementia remains largely unknown. Recently, lysosomal involvement in the pathogenesis of these disorders has been described. Improved knowledge of secondary events may have impact on diagnosis, staging, and follow-up of affected children. Importantly, new insights may provide indications about possible disease reversal upon treatment. A discussion about the CNS pathophysiology involvement in LSDs is the aim of this review. The lysosomal involvement in adult neurodegenerative diseases will also be briefly described.
Newborn screening for X-linked adrenoleukodystrophy (X-ALD) has until now been limited in implementation because of the lack of an accepted standard methodology. We have previously reported a technique using LC-MS/MS analysis that could provide the basis for screening of newborns for X-ALD. The target analyte diagnostic for X-ALD and other peroxisomal disorders of peroxisomal beta-oxidation is 1-hexacosanoyl-2-lyso-sn-3-glycero-phosphorylcholine (26:0-lyso-PC). We report here the validation of the analytical method using an authentic standard of the target compound. The method possesses sensitivity of <1.0fmole injected on column with a correlation coefficient (R(2)) of 0.9987. A tetradeuterated analog of 26:0-lyso-PC served as the internal standard. The sensitivity of this clinical method was confirmed using 17 newborn samples of individuals with peroxisomal disorders retrieved from state newborn screening programs. These samples were run masked with over 1000 newborn samples. All affected individuals were identified with one exception. One sample which was retrieved as an affected did not have the biochemical or genetic abnormality of X-ALD and thus is considered an error in sample identity. These studies clearly show that the method is highly sensitive and accurate in identifying individuals with a defect in peroxisomal beta-oxidation such as X-ALD.
Lysosomal storage diseases represent a group of about 50 genetic disorders caused by deficiencies of lysosomal and non-lysosomal proteins. Patients accumulate compounds which are normally degraded in the lysosome. In many diseases this accumulation affects various organs leading to severe symptoms and premature death. The revelation of the mechanism by which stored compounds affect cellular function is the basis for understanding pathophysiology underlying lysosomal storage diseases. In the past years it has become clear that storage compounds interfere with various processes on the cellular level. The spectrum covers e.g. receptor activation by non-physiologic ligands, modulation of receptor response and intracellular effectors of signal transduction cascades, impairment of autophagy, and others. Importantly, many of these processes are associated with accumulation of storage material in non-lysosomal compartments. Here we summarize current knowledge on the effects that storage material can elicit on the cellular level.
The lysosomal storage diseases have become models of the progress in the delineation of the molecular pathology of inherited metabolic disorders. It is, indeed, a fact that the recent advances in the characterization of the molecular biology of the lysosomal apparatus and its enzymatic defects have laid the foundation for the development of therapeutic endeavors for these disorders. The prospects for enzyme therapy will depend on the ingenuity to develop molecular and cellular strategies necessary to normalize the metabolism in these and possibly other metabolic disorders. This review (with 181 references) focusses on the past and recent achievements, as well as the current barriers encountered on the pathway toward enzyme therapy for the lysosomal storage diseases.
A profound deficiency (10- to 30-fold) of beta-galactosidase activity was found in tissues (liver, spleen, kidney, and brain) from two patients with generalized gangliosidosis; this deficiency is demonstrated as a failure to cleave both p-nitrophenyl-beta-D-galactopyranoside and ganglioside GM(1) labeled with C(14) in the terminal galactose. We believe that this enzymic defect is responsible for the accumulation of ganglioside GM(1) and is the fundamental enzyme defect in generalized gangliosidosis.
The Zellweger syndrome is a lethal hereditary disease characterized by the absence of peroxisomes (microbodies) in liver and kidney, and variable abnormalities in mitochondria. We show here that tissues from five infants that had died of this syndrome contain less than 10% of the normal levels of phosphatidylethanolamine plasmalogen (pPE), a major phospholipid component of cellular membranes. Heart and muscle, but not other tissues, also contain a substantial fraction of phosphatidylcholine plasmalogen (pPC), and this fraction is also strongly reduced in the Zellweger patients. No other abnormalities in cellular phospholipids were detected. Key enzymes of the biosynthesis of plasmalogens have previously been shown to be exclusively located in the peroxisomes of rodent liver and the microperoxisomes of rodent brain. We infer that the corresponding enzymes are also located in peroxisomes in man and that the absence of peroxisomes in Zellweger patients leads to their inability to synthesize plasmalogens. Our results support the notion that the biosynthetic role of peroxisomes in mammals has thus far been underestimated. We suggest that the defect in plasmalogen synthesis and possibly as yet unknown peroxisomal reactions are responsible for the diverse abnormalities observed in Zellweger patients.
The assay of plasma very long chain fatty acids (VLCFAs), developed in our laboratory in 1981, has become the most widely used procedure for the diagnosis of X-linked adrenoleukodystrophy (X-ALD) and other peroxisomal disorders. We present here our 17 years' experience with this assay. Three VLCFA parameters, the level of hexacosanoic acid (C26:0), the ratio of C26:0 to tetracosanoic acid (C24:0), and of C26:0 to docosanoic acid (C22:0), were measured in 1,097 males (hemizygotes) with X-ALD, 1,282 women heterozygous for this disorder, including 379 obligate heterozygotes, 797 patients with other peroxisomal disorders, and 29,600 control subjects. All X-ALD hemizygotes who had not previously received Lorenzo's oil or a diet with a high erucic acid content had increased VLCFA levels, but the application of a discriminant function based on all three measurements is required to avoid the serious consequences of a false-negative result. VLCFA levels are increased at day of birth, thus providing the potential for neonatal mass screening, are identical in the childhood and adult forms, and do not change with age. Eighty-five percent of obligate heterozygotes had abnormally high VLCFA levels, but a normal result does not exclude carrier status. VLCFA levels were increased in all patients homozygous for Zellweger syndrome, neonatal adrenoleukodystrophy, infantile Refsum's disease, and in patients with deficiencies of peroxisomal acyl-coenzyme A oxidase, bifunctional enzyme, and 3-oxoacyl-coenzyme A thiolase. In these patients the degree of VLCFA excess correlated with clinical severity.
Over 400 patients with lysosomal and peroxisomal storage diseases have received hematopoietic stem cell transplantation from normal donors. Without treatment, all of these diseases have an inexorable fate leading to central nervous system deterioration and early death. On the other hand, all of the engrafted hosts have had a remarkable positive clinical improvement in response to normalization of previously deficient enzymatic activity. Survival data for those engrafted indicates continued life-span as long as two decades beyond transplantation. The particular diseases treated in this way are included in this article. The specific indications and methods for transplantation are also included in this article.
Peroxisomes are single, membrane-bound organelles present in nearly all eukaryotic cells (Lazarow and Moser 1995). The polypeptide composition of the peroxisomal membrane is distinct from that of other organelles. The peroxisome matrix has more than 50 enzymes involved in numerous metabolic pathways. Biogenesis of peroxisomes appears to proceed by import of newly synthesized proteins from the cytoplasm into existing peroxisomes, which enlarge and divide. Most peroxisomal proteins carry a peroxisomal targeting signal, PTS1 or PTS2 for matrix enzymes and mPTS for membrane proteins (Dyer et al 1996; Gould et al 1989; Swinkels et al 1991). The peroxisome biogenesis disorders (PBD) are a group of lethal autosomal-recessive diseases with overlapping phenotypes including Zellweger syndrome, neonatal adrenoleukodystrophy and infantile Refsum disease (Lazarow and Moser 1995). Failure to assemble normal peroxisomes, with the concomitant loss of multiple peroxisomal enzyme activities, is the cellular hallmark. Somatic cell fusion studies indicate that there are at least 10 complementation groups for PBDs, with complementation group (CG) 1 accounting for more than half of all PBD patients. Recently, PEXI encoding a member of the AAA protein family of ATPases was found to be the gene responsible for CG 1 (Portsteffen et al 1997; Reuber et al 1997). We report a common PEXI gene mutation, G843D, in relation to the PBD phenotype in a series of unrelated German patients in CG 1.
Genetically determined human peroxisomal disorders are subdivided into two major categories: disorders of peroxisome biogenesis (PBD), in which the organelle is not formed normally, and those that involve a single peroxisomal enzyme. Twelve PBD have been identified, and the molecular defects have been defined in 10. All involve defects in the import of proteins into the organelle. Factors required for this import are now referred to as peroxins (PEX) and form the basis of a new and preferred classification system. The PBD are associated with four clinical phenotypes, named before their association with the organelle was recognized: Zellweger syndrome (ZS), neonatal adrenoleukodystrophy (NALD), infantile Refsum disease (IRD), and rhizomelic chondrodysplasia punctata (RCDP). The first three are associated with 9 of the 10 PEX defects that have been defined so far, and represent a clinical continuum with variant severity, with ZS the most severe, NALD intermediate, and IRD the least severe. RCDP is associated with PEX7. Genotype-phenotype correlations are complicated by the fact that the clinical manifestations of the ZS-NALD-IRD continuum can be mimicked by disorders that affect single enzymes of peroxisomal fatty acid oxidation, and PEX7 by disorders of plasmalogen synthesis enzymes. Furthermore, clinical manifestations of each of the PEX disorders may vary. Phenotypic expression varies with the nature of the mutation, the milder phenotypes being associated with mutations that do not abolish function completely, or with mosaicism. Definition of the molecular defects is of great value for genetic counseling and may be of aid in establishing prognosis.
Zellweger syndrome (ZS), neonatal adrenoleukodystrophy (NALD), and infantile Refsum disease (IRD) are clinically overlapping syndromes, collectively called "peroxisome biogenesis disorders" (PBDs), with clinical features being most severe in ZS and least pronounced in IRD. Inheritance of these disorders is autosomal recessive. The peroxisome biogenesis disorders are genetically heterogeneous, having at least 12 different complementation groups (CGs). The gene affected in CG1 is PEX1. Approximately 65% of the patients with PBD harbor mutations in PEX1. In the present study, we used SSCP analysis to evaluate a series of patients belonging to CG1 for mutations in PEX1 and studied phenotype-genotype correlations. A complete lack of PEX1 protein was found to be associated with severe ZS; however, residual amounts of PEX1 protein were found in patients with the milder phenotypes, NALD and IRD. The majority of these latter patients carried at least one copy of the common G843D allele. When patient fibroblasts harboring this allele were grown at 30 degrees C, a two- to threefold increase in PEX1 protein levels was observed, associated with a recovery of peroxisomal function. This suggests that the G843D missense mutation results in a misfolded protein, which is more stable at lower temperatures. We conclude that the search for the factors and/or mechanisms that determine the stability of mutant PEX1 protein by high-throughput procedures will be a first step in the development of therapeutic strategies for patients with mild PBDs.
Peroxisomes are subcellular organelles catalyzing a number of indispensable functions in cellular metabolism. The importance of peroxisomes is stressed by the existence of an expanding number of genetic diseases in which there is an impairment of one or more peroxisomal functions. The prototype of this group of diseases is the cerebro-hepato-renal syndrome of Zellweger (ZS), first described as a familial syndrome of multiple congenital defects in 1964. ZS is characterized by the presence of dysmorphias and polymalformative syndrome, severe neurologic abnormalities including neurosensory defects and hepato-intestinal dysfunction with failure to thrive and usually early death. Other peroxisomal disorders share some of these symptoms, but with varying degrees of organ involvement, severity of dysfunction and duration of survival. This paper provides an overview of the peroxisomal disorders including their clinical, biochemical and molecular characteristics with particular emphasis on the clinical presentation in neonates.
The peroxisome biogenesis disorders (PBDs) form a genetically and clinically heterogeneous group of disorders due to defects in at least 11 distinct genes. The prototype of this group of disorders is Zellweger syndrome (ZS) with neonatal adrenoleukodystrophy (NALD) and infantile Refsum disease (IRD) as milder variants. Common to PBDs are liver disease, variable neurodevelopmental delay, retinopathy and perceptive deafness. PBD patients belonging to complementation group 10 (CG10) have mutations in the PEX2 gene (PXMP3), which codes for a protein (PEX2) that contains two transmembrane domains and a zinc-binding domain considered to be important for its interaction with other proteins of the peroxisomal protein import machinery. We report on the identification of four PBD patients belonging to CG10. Sequence analysis of their PEX2 genes revealed 4 different mutations, 3 of which have not been reported before. Two of the patients had homozygous mutations leading to truncated proteins lacking both transmembrane domains and the zinc-binding domain. These mutations correlated well with their severe phenotypes. The third patient had a homozygous mutation leading to the absence of the zinc-binding domain (W223X) and the fourth patient had a homozygous mutation leading to the change of the second cysteine residue of the zinc-binding domain (C247R). Surprisingly, the patient lacking the domain had a mild phenotype, whereas the C247R patient had a severe phenotype. This might be due to an increased instability of PEX2 due to the R for C substitution or to a dominant negative effect on interacting proteins.
Mammals contain various cells differentiated in both morphology and function, which play vital roles in tissue-specific functions. Late endosome/lysosome and lysosomal-related organelles are involved in these specialized functions including antigen presentation, bone remodeling and hormone regulation. To fulfill these diverse roles, lysosomes are present at different levels in different tissues and cell types; however, their morphology within these different tissues varies and the regulation of their activities differs with lysosomal compartments in some cells also functioning as secretory compartments. The luminal acidification of these organelles is closely correlated with their functions. This review will discuss the functions of lysosomes and lysosomal-related organelles, with particular emphasis on the major proton pump, the vacuolar-type proton ATPase (V-ATPase), which is responsible for luminal acidification.
The group of peroxisomal disorders now includes 17 different disorders with Zellweger syndrome as prototype. Thanks to the explosion of new information about the functions and biogenesis of peroxisomes, the metabolic and molecular basis of most of the peroxisomal disorders has been resolved. A review of peroxisomal disorders is provided in this paper.
The peroxisome biogenesis disorders (PBDs) with generalized peroxisomal dysfunction include Zellweger syndrome (ZS), neonatal adrenoleukodystrophy (NALD), and infantile Refsum disease (IRD). There is clinical, biochemical, and genetic overlap among the three phenotypes, also known as Zellweger spectrum disorders. Clinical distinctions between the phenotypes are not sharply defined. Only limited sources are available to serve as a background for prognosis in PBD, especially in case of prolonged survival. We delineated the natural history of 31 PBD patients (age 1.2-24 years) through systematic clinical and biochemical investigations. We excluded classical ZS from our study, and included all patients with a biochemically confirmed generalized peroxisomal disorder over 1 year of age, irrespective of the previously diagnosed phenotype. The initial clinical suspicion, age at diagnosis, growth, development, neurological symptoms, organ involvements, and survival are summarized. Common to all patients were cognitive and motor dysfunction, retinopathy, sensorineural hearing impairment, and hepatic involvement. Many patients showed postnatal growth failure, 10 patients displayed hyperoxaluria of whom 4 had renal stones. Motor skills ranged from sitting with support to normal gait. Speech development ranged from non-verbal expression to grammatical speech and comprehensive reading. The neurodevelopmental course was variable with stable course, rapid decline with leukodystrophy, spinocerebellar syndrome, and slow decline over a wide range of faculties as outcome profiles. At the molecular level, 21 patients had mutations in the PEX1 gene. The two most common PEX1 mutations were the G843D (c.2528G-->A) missense and the c.2097insT frameshift mutation. Patients having the G843D/G843D or the G843D/c.2097insT genotypes were compared. Patients homozygous for G843D generally had a better developmental outcome. However, one patient who was homozygous for the "mild" G843D mutation had an early lethal disease, whereas two other patients had a phenotype overlapping with the G843D/c.2097insT group. This indicates that next to the PEX1 genotype other yet unknown factors determine the ultimate phenotype.
The peroxisomal disorders represent a group of genetic diseases in humans in which there is an impairment in one or more peroxisomal functions. The peroxisomal disorders are usually subdivided into two subgroups including (i) the peroxisome biogenesis disorders (PBDs) and (ii) the single peroxisomal (enzyme-) protein deficiencies. The PBD group is comprised of four different disorders including Zellweger syndrome (ZS), neonatal adrenoleukodystrophy (NALD), infantile Refsum's disease (IRD), and rhizomelic chondrodysplasia punctata (RCDP). ZS, NALD, and IRD are clearly distinct from RCDP and are usually referred to as the Zellweger spectrum with ZS being the most severe and NALD and IRD the less severe disorders. Studies in the late 1980s had already shown that the PBD group is genetically heterogeneous with at least 12 distinct genetic groups as concluded from complementation studies. Thanks to the much improved knowledge about peroxisome biogenesis notably in yeasts and the successful extrapolation of this knowledge to humans, the genes responsible for all these complementation groups have been identified making molecular diagnosis of PBD patients feasible now. It is the purpose of this review to describe the current stage of knowledge about the clinical, biochemical, cellular, and molecular aspects of PBDs, and to provide guidelines for the post- and prenatal diagnosis of PBDs. Less progress has been made with respect to the pathophysiology and therapy of PBDs. The increasing availability of mouse models for these disorders is a major step forward in this respect.