[Show abstract][Hide abstract] ABSTRACT: Objective
Deficiency of pyruvate dehydrogenase complex (PDHC) is the most common genetic disorder leading to lactic acidosis. PDHC deficiency is genetically heterogenous and most patients have defects in the X-linked E1-α gene but defects in the other components of the complex encoded by PDHB, PDHX, DLAT, DLD genes or in the regulatory enzyme encoded by PDP1 have also been found. Phenylbutyrate enhances PDHC enzymatic activity in vitro and in vivo by increasing the proportion of unphosphorylated enzyme through inhibition of pyruvate dehydrogenase kinases and thus, has potential for therapy of patients with PDHC deficiency. In the present study, we investigated response to phenylbutyrate of multiple cell lines harboring all known gene defects resulting in PDHC deficiency.Methods
Fibroblasts of patients with PDHC deficiency were studied for their enzyme activity at baseline and following phenylbutyrate incubation. Drug responses were correlated with genotypes and protein levels by Western blotting.ResultsLarge deletions affecting PDHA1 that result in lack of detectable protein were unresponsive to phenylbutyrate, whereas increased PDHC activity was detected in most fibroblasts harboring PDHA1 missense mutations. Mutations affecting the R349-α residue were directed to proteasome degradation and were consistently unresponsive to short-time drug incubation but longer incubation resulted in increased levels of enzyme activity and protein that may be due to an additional effect of phenylbutyrate as a molecular chaperone.InterpretationPDHC enzyme activity was enhanced by phenylbutyrate in cells harboring missense mutations in PDHB, PDHX, DLAT, DLD, and PDP1 genes. In the prospect of a clinical trial, the results of this study may allow prediction of in vivo response in patients with PDHC deficiency harboring a wide spectrum of molecular defects.
Annals of Clinical and Translational Neurology. 06/2014;
[Show abstract][Hide abstract] ABSTRACT: Mutations in the CACNA1A gene, encoding the α1 subunit of the voltage-gated calcium channel CaV2.1 (P/Q-type), have been associated with three neurological phenotypes: familial and sporadic hemiplegic migraine type 1 (FHM1, SHM1), episodic ataxia type 2 (EA2), and spinocerebellar ataxia type 6 (SCA6). We report a child with congenital ataxia, abnormal eye movements and developmental delay who presented severe attacks of hemiplegic migraine triggered by minor head traumas and associated with hemispheric swelling and seizures. Progressive cerebellar atrophy was also observed. Remission of the attacks was obtained with acetazolamide. A de novo 3bp deletion was found in heterozygosity causing loss of a phenylalanine residue at position 1502, in one of the critical transmembrane domains of the protein contributing to the inner part of the pore. We characterized the electrophysiology of this mutant in a Xenopus oocyte in vitro system and showed that it causes gain of function of the channel. The mutant CaV2.1 activates at lower voltage threshold than the wild type. These findings provide further evidence of this molecular mechanism as causative of FHM1 and expand the phenotypic spectrum of CACNA1A mutations with a child exhibiting severe SHM1 and non-episodic ataxia of congenital onset.
[Show abstract][Hide abstract] ABSTRACT: Recent advances in genetics led to significant improvement in the field of childhood epilepsies diagnosis and physiopathology. Genetic testing is indicated by geneticist who is himself guided by the pediatric neurological approach. In rare circumstance, genetic etiology affects the clinical management. Cost remains the main limitation. Those new genetic tools are the first step toward a better understanding of seizure mechanism and therefore more efficient treatments.
[Show abstract][Hide abstract] ABSTRACT: Mutations in the TMEM70 are the most common cause of nuclear ATP synthase deficiency resulting in a distinctive phenotype characterized by severe neonatal hypotonia, hypertrophic cardiomyopathy (HCMP), facial dysmorphism, severe lactic acidosis, hyperammonemia and 3-methylglutaconic aciduria (3-MGA).
We collected 9 patients with genetically confirmed TMEM70 defect from 8 different families. Six were homozygous for the c.317-2A>G mutation, 2 were compound heterozygous for mutations c.317-2A>G and c.628A>C and 1 was homozygous for the novel c.701A>C mutation. Generalized hypotonia, lactic acidosis, hyperammonemia and 3-MGA were present in all since birth. Five patients presented acute respiratory distress at birth requiring intubation and ventilatory support. HCMP was detected in 5 newborns and appeared a few months later in 3 additional children. Five patients showed a severe and persistent neonatal pulmonary hypertension (PPHN) requiring Nitric Oxide (NO) and/or sildenafil administration combined in 2 cases with high-frequency oscillatory (HFO) ventilation. In 3 of these patients, echocardiography detected signs of HCMP at birth.
PPHN is a life-threatening poorly understood condition with bad prognosis if untreated. Pulmonary hypertension has rarely been reported in mitochondrial disorders and, so far, it has been described in association with TMEM70 deficiency only in one patient. This report further expands the clinical and genetic spectrum of the syndrome indicating PPHN as a frequent and life-threatening complication regardless of the type of mutation. Moreover, in these children PPHN appears even in the absence of an overt cardiomyopathy, thus representing an early sign and a clue for diagnosis.
Molecular Genetics and Metabolism 01/2014; · 2.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Introduction
Mutations in the TMEM70 are the most common cause of nuclear ATP synthase deficiency resulting in a distinctive phenotype characterized by severe neonatal hypotonia, hypertrophic cardiomyopathy (HCMP), facial dysmorphism, severe lactic acidosis, hyperammonaemia and 3-methylglutaconic aciduria (3-MGA).
Methods and Results
We collected 9 patients with genetically confirmed TMEM70 defect from 8 different families. Six were homozygous for the c.317-2A > G mutation, 2 were compound heterozygous for mutations c.317-2A > G and c.628A > C and 1 was homozygous for the novel c.701A > C mutation. Generalized hypotonia, lactic acidosis, hyperammonaemia and 3-MGA were present in all since birth. Five patients presented acute respiratory distress at birth requiring intubation and ventilatory support. HCMP was detected in 5 newborns and appeared a few months later in 3 additional children. Five patients showed a severe and persistent neonatal pulmonary hypertension (PPHN) requiring Nitric Oxide (NO) and/or sildenafil administration combined in 2 cases with high-frequency oscillatory (HFO) ventilation. In 3 of these patients echocardiography detected signs of HCMP at birth.
PPHN is a life-threatening poorly understood condition with bad prognosis if untreated. Pulmonary hypertension has rarely been reported in mitochondrial disorders and, so far, it has been described in association with TMEM70 deficiency only in one patient. This report further expands the clinical and genetic spectrum of the syndrome indicating PPHN as a frequent and life-threatening complication regardless of the type of mutation. Moreover, in these children PPHN appears even in absence of an overt cardiomyopathy, thus representing an early sign and a clue for diagnosis.
Molecular Genetics and Metabolism 01/2014; · 2.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Genomic rearrangements at chromosome 13q31.3q32.1 have been associated with digital anomalies, dysmorphic features, and variable degree of mental disability. Microdeletions leading to haploinsufficiency of miR17∼92, a cluster of micro RNA genes closely linked to GPC5 in both mouse and human genomes, has recently been associated with digital anomalies in the Feingold like syndrome. Here, we report on a boy with familial dominant post-axial polydactyly (PAP) type A, overgrowth, significant facial dysmorphisms and autistic traits who carries the smallest germline microduplication known so far in that region. The microduplication encompasses the whole miR17∼92 cluster and the first 5 exons of GPC5. This report supports the newly recognized role of miR17∼92 gene dosage in digital developmental anomalies, and suggests a possible role of GPC5 in growth regulation and in cognitive development.
European journal of medical genetics 06/2013; · 1.57 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Kenny-Caffey syndrome (KCS) and the similar but more severe osteocraniostenosis (OCS) are genetic conditions characterized by impaired skeletal development with small and dense bones, short stature, and primary hypoparathyroidism with hypocalcemia. We studied five individuals with KCS and five with OCS and found that all of them had heterozygous mutations in FAM111A. One mutation was identified in four unrelated individuals with KCS, and another one was identified in two unrelated individuals with OCS; all occurred de novo. Thus, OCS and KCS are allelic disorders of different severity. FAM111A codes for a 611 amino acid protein with homology to trypsin-like peptidases. Although FAM111A has been found to bind to the large T-antigen of SV40 and restrict viral replication, its native function is unknown. Molecular modeling of FAM111A shows that residues affected by KCS and OCS mutations do not map close to the active site but are clustered on a segment of the protein and are at, or close to, its outer surface, suggesting that the pathogenesis involves the interaction with as yet unidentified partner proteins rather than impaired catalysis. FAM111A appears to be crucial to a pathway that governs parathyroid hormone production, calcium homeostasis, and skeletal development and growth.
The American Journal of Human Genetics 05/2013; · 11.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Proteoglycans (PGs) are a major component of the extracellular matrix in many tissues and function as structural and regulatory molecules. PGs are composed of core proteins and glycosaminoglycan (GAG) side chains. The biosynthesis of GAGs starts with the linker region that consists of four sugar residues and is followed by repeating disaccharide units. By exome sequencing, we found that B3GALT6 encoding an enzyme involved in the biosynthesis of the GAG linker region is responsible for a severe skeletal dysplasia, spondyloepimetaphyseal dysplasia with joint laxity type 1 (SEMD-JL1). B3GALT6 loss-of-function mutations were found in individuals with SEMD-JL1 from seven families. In a subsequent candidate gene study based on the phenotypic similarity, we found that B3GALT6 is also responsible for a connective tissue disease, Ehlers-Danlos syndrome (progeroid form). Recessive loss-of-function mutations in B3GALT6 result in a spectrum of disorders affecting a broad range of skeletal and connective tissues characterized by lax skin, muscle hypotonia, joint dislocation, and spinal deformity. The pleiotropic phenotypes of the disorders indicate that B3GALT6 plays a critical role in a wide range of biological processes in various tissues, including skin, bone, cartilage, tendon, and ligament.
The American Journal of Human Genetics 05/2013; · 11.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Glutaric aciduria type I (glutaryl-CoA dehydrogenase deficiency) is an inborn error of metabolism that usually manifests in infancy by an acute encephalopathic crisis and often results in permanent motor handicap. Biochemical hallmarks of this disease are elevated levels of glutarate and 3-hydroxyglutarate in blood and urine. The neuropathology of this disease is still poorly understood, as low lysine diet and carnitine supplementation do not always prevent brain damage, even in early-treated patients. We used a 3D in vitro model of rat organotypic brain cell cultures in aggregates to mimic glutaric aciduria type I by repeated administration of 1 mM glutarate or 3-hydroxyglutarate at two time points representing different developmental stages. Both metabolites were deleterious for the developing brain cells, with 3-hydroxyglutarate being the most toxic metabolite in our model. Astrocytes were the cells most strongly affected by metabolite exposure. In culture medium, we observed an up to 11-fold increase of ammonium in the culture medium with a concomitant decrease of glutamine. We further observed an increase in lactate and a concomitant decrease in glucose. Exposure to 3-hydroxyglutarate led to a significantly increased cell death rate. Thus, we propose a three step model for brain damage in glutaric aciduria type I: (i) 3-OHGA causes the death of astrocytes, (ii) deficiency of the astrocytic enzyme glutamine synthetase leads to intracerebral ammonium accumulation, and (iii) high ammonium triggers secondary death of other brain cells. These unexpected findings need to be further investigated and verified in vivo. They suggest that intracerebral ammonium accumulation might be an important target for the development of more effective treatment strategies to prevent brain damage in patients with glutaric aciduria type I.
PLoS ONE 01/2013; 8(1):e53735. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: BACKGROUND: Methylmalonic aciduria is an inborn error of metabolism characterized by accumulation of methylmalonate (MMA), propionate and 2-methylcitrate (2-MCA) in body fluids. Early diagnosis and current treatment strategies aimed at limiting the production of these metabolites are only partially effective in preventing neurological damage. METHODS: To explore the metabolic consequences of methylmalonic aciduria on the brain, we used 3D organotypic brain cell cultures from rat embryos. We challenged the cultures at two different developmental stages with 1 mM MMA, propionate or 2-MCA applied 6 times every 12 h. In a dose--response experiment cultures were challenged with 0.01, 0.1, 0.33 and 1 mM 2-MCA. Immunohistochemical staining for different brain cell markers were used to assess cell viability, morphology and differentiation. Significant changes were validated by Western blot analysis. Biochemical markers were analyzed in culture media. Apoptosis was studied by immunofluorescence staining and Western blots for activated caspase-3. RESULTS: Among the three metabolites tested, 2-MCA consistently produced the most pronounced effects. Exposure to 2-MCA caused morphological changes in neuronal and glial cells already at 0.01 mM. At the biochemical level the most striking result was a significant ammonium increase in culture media with a concomitant glutamine decrease. Dose--response studies showed significant and parallel changes of ammonium and glutamine starting from 0.1 mM 2-MCA. An increased apoptosis rate was observed by activation of caspase-3 after exposure to at least 0.1 mM 2-MCA. CONCLUSION: Surprisingly, 2-MCA, and not MMA, seems to be the most toxic metabolite in our in vitro model leading to delayed axonal growth, apoptosis of glial cells and to unexpected ammonium increase. Morphological changes were already observed at 2-MCA concentrations as low as 0.01 mM. Increased apoptosis and ammonium accumulation started at 0.1 mM thus suggesting that ammonium accumulation is secondary to cell suffering and/or cell death. Local accumulation of ammonium in CNS, that may remain undetected in plasma and urine, may therefore play a key role in the neuropathogenesis of methylmalonic aciduria both during acute decompensations and in chronic phases. If confirmed in vivo, this finding might shift the current paradigm and result in novel therapeutic strategies.
[Show abstract][Hide abstract] ABSTRACT: Spondylo-megaepiphyseal-metaphyseal dysplasia (SMMD; OMIM 613330) is a dysostosis/dysplasia caused by recessive mutations in the homeobox-containing gene, NKX3-2 (formerly known as BAPX1). Because of the rarity of the condition, its diagnostic features and natural course are not well known. We describe clinical and radiographic findings in six patients (five of which with homozygous mutations in the NKX3-2 gene) and highlight the unusual and severe changes in the cervical spine and the neurologic complications. In individuals with SMMD, the trunk and the neck are short, while the limbs, fingers and toes are disproportionately long. Radiographs show a severe ossification delay of the vertebral bodies with sagittal and coronal clefts, missing ossification of the pubic bones, large round "balloon-like" epiphyses of the long bones, and presence of multiple pseudoepiphyses at all metacarpals and phalanges. Reduced or absent ossification of the cervical vertebrae leads to cervical instability with anterior or posterior kinking of the cervical spine (swan neck-like deformity, kyknodysostosis). As a result of the cervical spine instability or deformation, five of six patients in our series suffered cervical cord injury that manifested clinically as limb spasticity. Although the number of individuals observed is small, the high incidence of cervical spine deformation in SMMD is unique among skeletal dysplasias. Early diagnosis of SMMD by recognition of the radiographic pattern might prevent of the neurologic complications via prophylactic cervical spine stabilization.
American Journal of Medical Genetics Part C Seminars in Medical Genetics 07/2012; 160C(3):230-7. · 3.54 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Progressive pseudorheumatoid dysplasia (PPRD) is a genetic, non-inflammatory arthropathy caused by recessive loss of function mutations in WISP3 (Wnt1-inducible signaling pathway protein 3; MIM 603400), encoding for a signaling protein. The disease is clinically silent at birth and in infancy. It manifests between the age of 3 and 6 years with joint pain and progressive joint stiffness. Affected children are referred to pediatric rheumatologists and orthopedic surgeons; however, signs of inflammation are absent and anti-inflammatory treatment is of little help. Bony enlargement at the interphalangeal joints progresses leading to camptodactyly. Spine involvement develops in late childhood and adolescence leading to short trunk with thoracolumbar kyphosis. Adult height is usually below the 3rd percentile. Radiographic signs are relatively mild. Platyspondyly develops in late childhood and can be the first clue to the diagnosis. Enlargement of the phalangeal metaphyses develops subtly and is usually recognizable by 10 years. The femoral heads are large and the acetabulum forms a distinct "lip" overriding the femoral head. There is a progressive narrowing of all articular spaces as articular cartilage is lost. Medical management of PPRD remains symptomatic and relies on pain medication. Hip joint replacement surgery in early adulthood is effective in reducing pain and maintaining mobility and can be recommended. Subsequent knee joint replacement is a further option. Mutation analysis of WISP3 allowed the confirmation of the diagnosis in 63 out of 64 typical cases in our series. Intronic mutations in WISP3 leading to splicing aberrations can be detected only in cDNA from fibroblasts and therefore a skin biopsy is indicated when genomic analysis fails to reveal mutations in individuals with otherwise typical signs and symptoms. In spite of the first symptoms appearing in early childhood, the diagnosis of PPRD is most often made only in the second decade and affected children often receive unnecessary anti-inflammatory and immunosuppressive treatments. Increasing awareness of PPRD appears to be essential to allow for a timely diagnosis.
American Journal of Medical Genetics Part C Seminars in Medical Genetics 07/2012; 160C(3):217-29. · 3.54 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We report on a consanguineous, Afghani family with two sisters affected with characteristic facial features, multiple contractures, progressive joint and skin laxity, hemorrhagic diathesis following minor trauma and multisystem fragility-related manifestations suggestive of a diagnosis of musculocontractural Ehlers-Danlos syndrome (EDS). This novel form of connective tissue disorder was recently reported in patients of Japanese, Turkish, and Indian descent who were formerly classified as having EDS type VIB and has now been recognized to be a part of spectrum including patients previously classified as having adducted thumb-clubfoot syndrome. We identified a previously unreported mutation in the CHST14 gene, which codes for the enzyme dermatan 4-O-sulfotransferase. We discuss the prenatal presentation, detailed clinical manifestations, and neurological findings in two sisters with this newly described musculocontractural EDS-CHST14 type. We demonstrate that fibroblasts from one of our patients produce more chondroitin sulfate than normal and show lower than normal deposition of collagens I and II and fibrillin 1-containing microfibrills. These findings suggest that the imbalance in the glycosaminoglycan content in developing tissues might interfere with normal deposition of other extracellular matrix components and ultimately contribute to the development of the phenotype observed in these patients. Furthermore, we ruled out the contribution of intrinsic platelet factors to the bleeding diathesis observed in some affected individuals.
American Journal of Medical Genetics Part A 05/2012; 158A(6):1344-54. · 2.30 Impact Factor