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Inborn Errors of Carbohydrate, Ammonia, Amino Acid, and Organic Acid Metabolism
... PCD type A, also called the North American type, is characterized by severe symptoms that begin in infancy. Features include developmental delay, hypoglycemia, and lactic acidosis, which causes vomiting, abdominal pain, muscle weakness, and fatigue [5]. Type B, also called neonatal or French form, usually presents within the first 72 hours of life. ...
... Type B, also called neonatal or French form, usually presents within the first 72 hours of life. This type is characterized by severe lactic acidosis, hyperammonemia, truncal hypotonia, coma, and liver failure [5]. Type C, the benign variety, is extremely rare, and it is characterized by a normal or slight increase in lactic acid levels, with little impact on the nervous system [2,6]. ...
Pyruvate carboxylase (PC) converts pyruvate to oxaloacetate, which is an important step in gluconeogenesis. Pyruvate carboxylase deficiency (PCD) is a rare inherited metabolic disorder characterized by movement disorders, neurologic disturbances, hypoglycemia, lactic acidosis, hyperammonemia, and elevated levels of pyruvate and alanine in plasma. The prognosis for PCD is poor. Most children die within the first six months of life, and those who survive longer have neurological damage and mental disability. This is due to the accumulation of lactic acid and toxic components in the blood. Here we describe the case of a 21-month-old male presenting with abnormal movements and new-onset seizures. His family history is relevant because of parental consanguinity. A genetic analysis showed a novel mutation, homozygous c. 2630A>G (p. Gln877Arg) variant, in the PC gene, a mutation not previously described in the English literature.
... Deficiency of the enzymes in both type Ia and Ib cause inadequate hepatic conversion of glucose-6-phosphate to glucose through normal glycogenolysis and gluconeogenesis, leading to fasting hypoglycemia. 1,2 The genes for glucose-6-phosphatase and translocase are located on chromosomes 17q21 and 11q23, respectively. Common pathogenic variants have been identified. ...
Background: Conversion of glucose-6-phosphate to glucose is the final step in both glycogenolysis and gluconeogenesis. In glycogen storage disease type Ia (GSD type Ia), decreased activity of the enzyme glucose6-phosphatase leads to an increased concentration of glucose-6- phosphate within the hepatocytes and shunting into alternative pathway with the following consequences: hyperlactatemia, hyperuricemia and hypertriglyceridemia. Patients develop hypoglycemia within 3 to 4 hours after a meal. Case Report: We reported four patients with GSD type Ia with different clinical manifestations such as hypoglycemia, hepatomegaly, lactic acidosis, hyperchylomicronemia, and hyperuricemia and also described their prognosis. Conclusion: Previously, many children with GSD Ia died in infancy or early childhood. Recurrent severe hypoglycemia can cause brain damage, but the prognosis has improved dramatically with early diagnosis and long term maintenance of optimal metabolic control.
... Different information is also observed as to how many phenotypes it is. According to Cederbaum, Berry, 2012 there are 2 major phenotypes: an acute form manifests as catastrophic disease in the newborn period, and the late-onset type is characterized by chronic, intermittent episodes of metabolic decompensation. The degree of enzyme deficiency and the mutations differ between the two extreme presentations. ...
Introduction: The specialized physiotherapy program is a set of purposeful techniques and methodologies, profiled for work with children. Early physical therapy intervention is essential for the prevention and reduction of the pathological impact on the neuromotor capabilities of children with neurological impairment caused by a genetic disease. Purpose: The aim of the study is to monitor the effectiveness of a specialized physiotherapy program in a child with a deviation in neuromotor development. The therapy was performed 5 times a week for 3 months. The object of the study is the influence of physiotherapy in case of deviation in the neuromotor development of an infant with a rare genetic disease. The contingent of the study is 1 infant with a rare genetic disease - isovaleric acidemia and is the only case of a patient with such a disease in Bulgaria. The infant is 9 months old (7 adjusted months). The deviations are expressed in pathologically amplified and persistent primitive reflexes and delay in motor development. We assessed gross motor development by the method of Gross Motor Function Measure – 88 in the beginning and then made a reassessment on the 3rd month from the beginning of the therapy. Results: The analysis of the results shows that the specialized physiotherapy program influenced the neuromotor development of the patient - helping to integrate primitive reflexes; to develop and improve motor skills. Conclusions: Specialized physiotherapy is an effective treatment for neuromotor deviation in infant with a rare genetic disease.
... (12). Defects within the E1 α-subunit of the PDH enzyme arise from nonsense/ missense and deletion/insertion pathogenic variants in the PDHA1 gene found on the X chromosome (13,14). A study with 130 patients from 123 unrelated families by Lissens et al., found that most female patients have deletion/insertion pathogenic variants occurring in exons 10 and 11; while most male patients manifest nonsense/missense pathogenic variants occurring in exons 3,7,8 and 11 (13). ...
Pyruvate dehydrogenase (PDH) deficiency is caused by a number of pathogenic variants
and the most common are found in the PDHA1 gene. The PDHA1 gene encodes one of the
subunits of the PDH enzyme found in a carbohydrate metabolism pathway involved in
energy production. Pathogenic variants of PDHA1 gene usually impact the α-subunit of
PDH causing energy reduction. It potentially leads to increased mortality in sufferers.
Potential treatments for this disease include dichloroacetate and phenylbutyrate,
previously used for other diseases such as cancer and maple syrup urine disease.
However, not much is known about their efficacy in treating PDH deficiency. Effective
treatment for PDH deficiency is crucial as carbohydrate is needed in a healthy diet and rice
is the staple food for a large portion of the Asian population. This review analysed the
efficacy of dichloroacetate and phenylbutyrate as potential treatments for PDH deficiency
caused by PDHA1 pathogenic variants. Based on the findings of this review,
dichloroacetate will have an effect on most PDHA1 pathogenic variant and can act as
a temporary treatment to reduce the lactic acidosis, a common symptom of PDH
deficiency. Phenylbutyrate can only be used on patients with certain pathogenic
variants (p.P221L, p.R234G, p.G249R, p.R349C, p.R349H) on the PDH protein. It is
hoped that the review would provide an insight into these treatments and improve the
quality of lives for patients with PDH deficiency.
... Pyruvate dehydrogenase is an enzyme of the tricarboxylic acid cycle that uses biotin as a cofactor. This enzyme does not function without biotin, so lactate levels increase as a consequence of BD (9). BD is also the major cause of late-onset biotin-responsive multiple carboxylase deficiency. ...
Background:
Biotinidase deficiency (BD) is a rare, inherited autosomal recessive disorder that is treatable within childhood. We present a patient with pneumonia and respiratory acidosis who was not diagnosed with any systemic disorders; the patient was finally diagnosed as BD.
Case report:
A thirty-year-old woman was admitted to the emergency department with respiratory failure that had persisted for a few days and progressively weakening over the previous six months. Then, the patient was admitted to the intensive care unit with marked respiratory acidosis, respiratory failure and alterations in consciousness. At the follow-up, the patient was not diagnosed with a systematic disorder. Rather, the patient's historical clinical findings suggested a metabolic disorder. Finally, the patient was diagnosed with biotinidase deficiency.
Conclusion:
Even though biotinidase deficiency is not frequently seen in the intensive care unit, metabolic syndromes such as biotinidase deficiency should be considered. Patients should be evaluated holistically with attention to medical history, family history and clinical findings.
... In some patients, this disorder may be diagnosed as late as 5 years [8] . However, hematologic problems are not observed at that age. ...
Aim:
Newborns with inborn errors of metabolism can present with hyperammonaemic coma. In this study, we evaluated the effect of peritoneal dialysis on plasma ammonium levels and on the short-term outcome in neonatal patients with urea cycle defects and organic acidaemia.
Methods:
Data from infants with hyperammonaemia due to urea cycle defects or organic acidaemia treated with dialysis were collected and retrospectively analysed. The results of patient groups (group I, survived; and group II, died) were compared.
Results:
Fourteen neonates were enrolled in this study. In group I, plasma ammonium levels before dialysis were median (IQR) 1652 μg/dl (1165-2098 μg/dl); in group II, they were 1289 μg/dl (1070-5550 μg/dl). There was no statistically significant difference. Urea cycle defects were diagnosed in eight, and organic acidaemia in six patients. The duration of a blood ammonia level >200 μg/dl was longer in group II (p=0.04). A <60.8 % decline in the ammonia level from the beginning of dialysis to the 12th hour of dialysis carried a 3.33-fold higher risk of mortality, when compared with a greater decline. Five patients with urea cycle defects, and one with organic acidaemia, died. The mortality risk was 8.33-fold (95% CI=0.63-90.86) higher for patients with urea cycle defects than for those with organic acidaemia.
Conclusion:
In patients with hyperammonaemia treated with peritoneal dialysis, the rate of ammonia removal and the underlying aetiology appear to be important prognostic factors. Neonates with organic acidaemia who are admitted to centres without continuous renal replacement therapy facilities can be effectively treated with peritoneal dialysis.
Asparagine synthetase deficiency is a rare inborn error of metabolism caused by a defect in ASNS, a gene encoding asparagine synthetase. It manifests with a severe neurological phenotype manifesting as severe developmental delay, congenital microcephaly, spasticity and refractory seizures. To date, nineteen patients from twelve unrelated families have been identified. Majority of the mutations are missense and nonsense mutations in homozygous or compound heterozygous state. We add another case from India which harbored a novel homozygous missense variation in exon 11 and compare the current case with previously reported cases.
The relationship between chromatographic resolution and amide structure of chiral 2-hydroxy acids as O-(−)-menthoxycarbonylated diastereomeric derivatives on achiral gas chromatography was investigated to elucidate the best diastereomeric conformation for enantiomeric separation of chiral 2-hydroxy acids. Thirteen chiral 2-hydroxy acids were converted into nine different diastereomeric O-(−)-menthoxycarbonylated amide derivatives using the primary, secondary and cyclic amines to achieve complete enantiomeric separation through an achiral column. Each enantiomeric pair of 2-hydroxy acids as O-(−)-menthoxycarbonylated tert-butylamide derivatives was resolved on both the DB-5 and DB-17 columns with resolution factors ranging from 1.7 to 4.8 and 1.7 to 3.4, respectively. The results revealed that the structure of the amide moiety is shown to significantly affect chromatographic resolution. In addition, O-(−)-menthoxycarbonylated tert-butylamide derivatives were shown to be the best diastereomeric conformations for enantiomeric separation of 2-hydroxy acids.
When comparing with our previous O-trifluoroacetylated(−)-menthyl ester derivatization method, the present results suggested that size differences between groups attached to the chiral center and conformational rigidity can have stronger effects on resolution than the distance between chiral centers. The elution of R- and S-stereoisomers was affected by the class of amine; i.e., primary, secondary, or cyclic, regardless of the substituents on the amine group, the structure of the 2-hydroxy acid, and the polarity of the column.
Childhood-onset mitochondrial encephalomyopathies are usually severe, relentlessly progressive conditions that have a fatal outcome. However, a puzzling infantile disorder, long known as 'benign cytochrome c oxidase deficiency myopathy' is an exception because it shows spontaneous recovery if infants survive the first months of life. Current investigations cannot distinguish those with a good prognosis from those with terminal disease, making it very difficult to decide when to continue intensive supportive care. Here we define the principal molecular basis of the disorder by identifying a maternally inherited, homoplasmic m.14674T>C mt-tRNA(Glu) mutation in 17 patients from 12 families. Our results provide functional evidence for the pathogenicity of the mutation and show that tissue-specific mechanisms downstream of tRNA(Glu) may explain the spontaneous recovery. This study provides the rationale for a simple genetic test to identify infants with mitochondrial myopathy and good prognosis.
Reports of the use of multiplex enzyme assay screening for Pompe disease, Fabry disease, Gaucher disease, Niemann-Pick disease types A and B, and Krabbe disease have engendered interest in the use of this assay in newborn screening. We modified the assay for high-throughput use in screening laboratories.
We optimized enzyme reaction conditions and procedures for the assay, including the concentrations of substrate (S) and internal standard (IS), assay cocktail compositions, sample clean-up procedures, and mass spectrometer operation. The S and IS for each enzyme were premixed and bottled at an optimized molar ratio to simplify assay cocktail preparation. Using the new S:IS ratio, we validated the modified assay according to CLSI guidelines. Stability of the S, IS, and assay cocktails were investigated. Dried blood spots from 149 healthy adults, 100 newborns, and 60 patients with a lysosomal storage disorder (LSD) were tested using the modified assay.
In our study, the median enzyme activity measured in adults was generally increased 2-3-fold compared to the original method, results indicating higher precision. In the multiplex format, each of the 5 modified enzyme assays enabled unambiguous differentiation between samples from healthy individuals (adults and newborns) and the corresponding disease-specific samples.
The modified multiplex enzyme assay with premixed S and IS is appropriate for use in high-throughput screening laboratories.
MAPLE syrup urine disease is a rare inborn error of branched-chain amino acid and branched-chain keto acid metabolism due to decreased branched-chain α-keto acid dehydrogenase-complex activity.1 The branched-chain keto acids, which are the substrates in this irreversible enzyme reaction, are derived from transamination of the branched-chain amino acids leucine, isoleucine, and valine. Consumption of branched-chain amino acids in the form of dietary protein in excess of an age-dependent daily requirement for protein synthesis results in the accumulation of branched-chain amino acids and branched-chain keto acids in the tissues and body fluids of patients in whom there is little or no . . .
Skeletal muscle mtDNA of three patients with mitochondrial encephalomyopathy, characterized clinically by myoclonic epilepsy and ragged-red fiber (MERRF) syndrome, has been sequenced to determine the underlying molecular defect(s). An A-to-G substitution of nt 8344 in the tRNA(Lys) gene, a substitution suggested to be associated with MERRF encephalomyopathy, was detected in these patients. Abnormal patterns of mitochondrial translation products were observed in the skeletal muscle of patients, consistent with the expected consequential defect in protein synthesis. The genealogical studies of the three patients, as well as mtDNA from one published MERRF patient and from nine other normal and disease controls, revealed that the tRNA(Lys) mutations in the MERRF patients have arisen independently. These observations provided evidence that the base substitution is a causal mutation for MERRF.
Clinical course, diagnostic and therapeutic management, and neurodevelopmental outcome were evaluated in 11 patients with glutaryl-coenzyme A dehydrogenase deficiency. In 9 patients macrocephalus was present at or shortly after birth and preceded the neurological disease. In 7 children an acute illness resembling encephalitis appeared after a period of normal development; 2 had developmental delay and progressive "dystonic cerebral palsy." Later, all 9 displayed typical signs of a disorder of the basal ganglia. In 1 patient with macrocephalus the disorder was diagnosed before the onset of neurological disease; in another it was diagnosed prenatally. Computed tomography and magnetic resonance imaging scans revealed severe generalized cerebral atrophy, most striking in the frontal and temporal lobes in 10 patients. Further deterioration was halted after initiation of treatment consisting of low-protein diets, special formulas low in lysine and tryptophan, and supplements of riboflavin and L-carnitine. Only 1 patient showed a slight clinical improvement. Later, dietary therapy was discontinued in 2 older patients and relaxed in a third without observed adverse effects. Two patients in whom treatment could be initiated before the onset of neurological symptoms have developed normally. However, duration of follow-up (6 and 29 months) does not yet allow classification of glutaryl-coenzyme A dehydrogenase deficiency as a treatable disorder. Total body production of glutaric acid, reflected in the daily urinary output, was efficiently reduced by therapeutic measures. Levels of glutaric acid in plasma and cerebrospinal fluid remained unchanged, which may in part explain the overall unsatisfactory outcome. All patients presented with a severe secondary deficiency of carnitine.(ABSTRACT TRUNCATED AT 250 WORDS)
IN adults, deficiency of carnitine palmitoyltransferase (CPT) II is a genetic disorder characterized by exercise intolerance and myoglobinuria.1 , 2 In newborns, it is a generalized, lethal disease with reduced CPT II activity in multiple organs, reduced concentrations of total and free carnitine, and increased concentrations of lipids and long-chain acylcarnitines.3 The clinical severity of CPT II deficiency is not determined by the degree of the reduction in CPT II activity, since this reduction is of similar magnitude in adults, young children, and newborns.1 2 3 4 5 However, lethal CPT II deficiency is associated with an accumulation of arrhythmogenic long-chain acylcarnitines,6 , 7 as in the patient . . .
Observations are reported of a patient afflicted with a disease previously unknown to us. The outstanding features of the syndrome are: onset in the neonatal period of episodes of vomiting, lethargy and ketosis; neutropenia; periodic thrombocytopenia; hypogammaglobulinemia; hyperglycinemia and hyperglycinuria; developmental retardation; and intolerance of protein of more than approximately 0.5 gm/kg of body weight/day and of protein hydrolysate and of leucine.
Fourteen hereditary disorders of fatty acid oxidation have been recognized within the last two decades. They can cause clinical symptoms ranging from antenatal manifestations such as malformations to neonatal acidotic coma, hypoglycemia, Reye syndrome-like episodes, sudden infant death, myopathy, cardiomyopathy, heartbeat disorders, myoglobinuria, retinitis pigmentosa, peripheral neuropathy, and renal manifestations. These inborn errors deserve prompt recognition since they can often be treated. Their overlapping clinical spectrum results in part from the accumulation of related toxic compounds, proximal to the metabolic block, and in part from the deficiency in energy production from fatty adds, ensuing distally from the defect in liver, myocardium, and skeletal muscle. This article reviews the pathophysiology and clinical presentation of known inborn errors of fatty acid catabolism. A summary of our experience with 84 patients, together with proposals for the diagnosis and therapeutic approach to these disorders, is presented.
Mantovani et al1 have recently reported the occurrence of pseudotumor cerebri and computed tomographic (CT) abnormalities in two patients with classic maple syrup urine disease (MSUD). We have observed the same CT abnormalities and clinical evidence of cerebral edema in a 12-day-old boy with MSUD, and suggest that this complication may in fact be more common than usually believed.
Report of a Case.—A boy was born following an uncomplicated pregnancy and delivery, weighing 3,200 g; head circumference (HC) was 35 cm at birth. He was well until the fifth day of life when lethargy, poor feeding, and vomiting appeared. Despite progression of the symptoms, he cranial pressure may partially be compensated for by the distensible skull of the neonate and thus be overlooked on clinical examination alone; only recently have CT-scan facilities become available; and the disease is so rare that it is only sporadically observed in most
Six inherited disorders of the urea cycle are well described (Fig. 20.1). These are the deficiencies of carbamoyl phosphate synthetase (CPS), ornithine transcarbamoylase (OTC), argininosuccinate synthetase, argininosuccinate lyase, arginase, and N-acetylglutamate synthetase (NAGS). Deficiencies of glutamine synthetase and of citrin have also been described. All these defects are characterised by hyperammonaemia and disordered amino acid metabolism. The presentation is highly variable: those presenting in the newborn period usually have an overwhelming illness that rapidly progresses from poor feeding, vomiting, lethargy or irritability and tachypnoea to fits, coma and respiratory failure. In infancy, the symptoms are less severe and more variable. Poor developmental progress, behavioural problems, hepatomegaly and gastrointestinal symptoms are common. Children and adults frequently have a chronic neurological illness that is characterised by variable behavioural problems, confusion, irritability and episodic vomiting. However, during any metabolic stress the patients may become acutely unwell. Arginase deficiency has more specific symptoms, such as spastic diplegia, dystonia, ataxia and fits. All these disorders have autosomal- recessive inheritance except ornithine transcarbamoylase deficiency, which is X-linked.
Respiratory chain deficiencies have long been regarded as neuromuscular diseases only. However, oxidative phosphorylation (i.e. ATP synthesis by the respiratory chain) is not restricted to the neuromuscular system but proceeds in all cells that contain mitochondria (Fig. 15.1). Most non-neuromuscular organs and tissues are, therefore, also dependent upon mitochondrial energy supply. Due to the twofold genetic origin of respiratory enzymes [nuclear DNA and mitochondrial (mtDNA)], a respiratory chain deficiency can theoretically give rise to any symptom in any organ or tissue at any age and with any mode of inheritance.
The diagnosis of a respiratory chain deficiency is difficult to consider initially when only one abnormal symptom is present. In contrast, this diagnosis is easier to consider when two or more seemingly unrelated symptoms are observed. The treatment, mainly dietetic, does not markedly influence the usually unfavorable course of the disease.
More than a dozen genetic defects in the fatty acid oxidation pathway are currently known. Nearly all of these defects present in early infancy as acute life-threatening episodes of hypoketotic, hypoglycemic coma induced by fasting or febrile illness (for recent reviews, see [1] [2] [3] [4]). In some of the disorders there also may be chronic skeletal muscle weakness or acute exerciseinduced rhabdomyolysis and acute or chronic cardiomyopathy. Recognition of the fatty acid oxidation disorders is often difficult because patients can appear well until exposed to prolonged fasting, and screening tests of metabolites may not always be diagnostic. Rare related disorders include a transport defect of fatty acids, and secondary (as in the Sjögren-Larsson syndrome), or primary defects in the metabolism of leukotrienes.
Three inborn errors of galactose metabolism are known. The most important is classic galactosemia due to galactose-1-phosphate uridyltransferase (GALT) deficiency. A complete or near-complete deficiency is life threatening with multiorgan involvement and long-term complications [1]. Partial deficiency is usually, but not always, benign. Uridine diphosphate galactose 4-epimerase (GALE) deficiency exists in at least two forms. The very rare profound deficiency clinically resembles classical galactosemia. The more frequent partial deficiency is usually benign. Galactokinase (GALK) deficiency is extremely rare and the most insidious, since it results in the formation of nuclear cataracts without provoking symptoms of intolerance. The Fanconi- Bickel syndrome (Chap. 11) is a congenital disorder of galactose transport due to GLUT2 deficiency leading to hypergalactosemia. Other secondary causes of impaired liver handling of galactose in the neonatal period are congenital portosystemic shunting and multiple hepatic arteriovenous malformations.
The liver GSDs comprise GSD I, the hepatic presentations of GSD III, GSD IV, GSD VI, the liver forms of GSD IX, and GSD 0. GSD I, -III, -VI, and -IX present with hypoglycaemia, marked hepatomegaly, and retarded growth [6]. GSD I is the most severe of these four conditions, because both glycogenolysis and gluconeogenesis are impaired. Patients with GSD III have a syndrome that includes hepatopathy, myopathy and often cardiomyopathy. Unlike the other hepatic forms of GSD, GSD IV usually manifests in infancy or childhood as hepatic failure with cirrhosis leading to end-stage liver disease. GSD VI and the hepatic forms of GSD IX are classically the mildest forms, but there is recent evidence that optimised therapy decreases the rate of liver pathology and improves growth.
Branched-chain organic acidurias or organic acidaemias are a group of disorders that result from an abnormality of specific enzymes involving the catabolism of branched-chain amino acids (BCAAs). Collectively, the most commonly encountered are maple syrup urine disease (MSUD), isovaleric aciduria (IVA), propionic aciduria (PA) and methyl malonic aciduria (MMA). They can present clinically as a severe neonatal-onset form of metabolic distress, an acute and intermittent late-onset form, or a chronic progressive form presenting as hypotonia, failure to thrive, and developmental delay. Other rare disorders involving leucine, isoleucine, and valine catabolism are 3-methylcrotonyl glycinuria, 3-methylglutaconic (3-MGC) aciduria, short-/branched-chain acyl-CoA dehydrogenase deficiency, 2-methyl-3-hydroxybutyryl-CoA dehydrogenase deficiency, isobutyryl-CoA dehydrogenase deficiency, 3-hydroxyisobutyric aciduria, and malonic aciduria.
Of 31 infants known to be at risk for a urea cycle defect because of family history, 18 were treated prospectively from birth with a disease-specific diagnostic and therapeutic protocol. Diagnosis was made on the basis of plasma citrulline and ASA levels over the first 72 hrs of life. Of the 7 affected infants in the prospectively treated group (OTC-3; CPS-1 AS-2; AL-1), one OTCD infant died (peak NH4 850uM) and 6 survived the neonatal period .(peak NH4 52-197uM). One OTCD survivor died at 33mos; 5 remain on therapy (ages 18-60mos). Developmental quotients for survivors range from 55-101. 16 prospectively-treated unaffected infants are normal at 9-60mos and show no ill effects from 4 days of therapy. In addition, 7 affected infants (OTC-4; CPS-2.; AS-1) were managed outside the protocol with observation, protein-restriction and/or IV benzoate and arginine and peritoneal dialysis after the onset of symptomatic hyperammonemia. Diagnosis was made 25-90hrs after birth. All 4 OTCD infants expired (2 were untreated). The 3 survivors are now 18-48 mos and remain on therapy. Peak neonatal ammonium levels ranged from 210-364uM. DQ scores in the CPSD patients are 99 and 133, while the ASD patient has a score of 55.
The mitochondrial deoxyribonucleotide (dNTP) pool is separated from the cytosolic pool because the mitochondria inner membrane is impermeable to charged molecules. The mitochondrial pool is maintained by either import of cytosolic dNTPs through dedicated transporters or by salvaging deoxynucleosides within the mitochondria; apparently, enzymes of the de novo dNTP synthesis pathway are not present in the mitochondria. In non-replicating cells, where cytosolic dNTP synthesis is down-regulated, mtDNA synthesis depends solely on the mitochondrial salvage pathway enzymes, the deoxyribonucleosides kinases. Two of the four human deoxyribonucleoside kinases, deoxyguanosine kinase (dGK) and thymidine kinase-2 (TK2), are expressed in mitochondria. Human dGK efficiently phosphorylates deoxyguanosine and deoxyadenosine, whereas TK2 phosphorylates deoxythymidine, deoxycytidine and deoxyuridine. Here we identify two mutations in TK2, histidine 90 to asparagine and isoleucine 181 to asparagine, in four individuals who developed devastating myopathy and depletion of muscular mitochondrial DNA in infancy. In these individuals, the activity of TK2 in muscle mitochondria is reduced to 14-45% of the mean value in healthy control individuals. Mutations in TK2 represent a new etiology for mitochondrial DNA depletion, underscoring the importance of the mitochondrial dNTP pool in the pathogenesis of mitochondrial depletion.
Pompe disease (acid maltase deficiency; glycogen storage disease type II) is caused by deficiency of the lysosomal enzyme acid alpha-glucosidase (GAA). Our clinical laboratory began to offer a fluorometric dried blood spot (DBS)-based GAA activity assay for Pompe disease in 2006 after the FDA approved GAA enzyme replacement therapy in April of that year. The purpose of this study was to examine the experience of our clinical laboratory in using this assay. Over a 2-year period, we received samples for the DBS GAA assay from 891 patients referred for possible Pompe disease, of whom 111 (12.5%) patients across the disease spectrum who had results in the affected range. The majority of the patients were referred by neurologists and geneticists. When available, we correlated the results obtained through DBS GAA activity assay with the results from a second DBS, or a second tissue (cultured skin fibroblasts or muscle biopsy). In our experience, the DBS GAA activity assay provides a robust, rapid, and reliable first tier test for screening patients suspected of having Pompe disease.
Mitochondria are cytoplasmic organelles in eukaryotic cells that accomplish several distinct vital functions, including oxidative phosphorylation, metabolic anaplerotic and degradative pathways, and integration of signaling for apoptosis. Impaired oxidative phosphorylation, the common final pathway of mitochondrial metabolism, results in a variety of clinical manifestations, and the term mitochondrial disorders is currently ascribed to (mostly) genetic diseases of the respiratory chain associated with mitochondrial DNA mutation or nuclear DNA mutations. Genetic disorders with impaired oxidative phosphorylation are extremely heterogeneous, as their clinical presentation ranges from lesions of single tissues or specialized structures, such as the optic nerve in the mitochondrial DNA-associated Leber's hereditary optic neuropathy and in the nuclear DNA-associated dominant optic atrophy, to more widespread pathologies, including myopathies, peripheral neuropathies, encephalomyopathies, cardiopathies, or complex multisystem disorders. The age at onset ranges from neonatal to adult life. This review focuses on mitochondrial diseases that find significant expression outside the central nervous system and the peripheral neuromuscular system, and manifest with substantial clinical signs and symptoms in tissues and organs such as the heart, endocrine system, liver, kidney, blood, and gastrointestinal tract. The available information on putative genotype-phenotype correlations and the related pathogenic mechanisms are summarized when appropriate.
The goals were to examine the frequency of perinatal manifestations of mitochondrial oxidative phosphorylation disorders within a population-based cohort, to characterize these manifestations, to identify a possible association between these manifestations and diagnoses at a later age, and to identify possible associations between perinatal complications and specific disorders.
We conducted a retrospective review of clinical and laboratory records for all patients with definitive oxidative phosphorylation disorders who were diagnosed and treated at the Royal Children's Hospital in Melbourne between 1975 and 2006 (N = 107; male/female ratio: 1.41).
Neonatal presentation was recorded for 32 of 107 patients (male/female ratio: 1:1), including 19 who presented on day 1 of life. Prematurity (gestational age of <37 weeks) was noted for 12.6% of the 107 patients. Of the 85 infants with known birth weights, 24 were in the <or=10th percentile for gestational age (11 with complex I deficiency), and 9 of those (6 with complex I deficiency) were in the <3rd percentile. The most common presenting neonatal symptoms after the first day of life were poor feeding, recurrent vomiting, and failure to thrive. We noted 3 main clinical neonatal forms of oxidative phosphorylation disorders (encephalomyopathic, hepatointestinal, and cardiac). Of the 32 infants, 28 died (13 in the neonatal period). Complex I deficiency was identified for 15 neonates, combined complexes I, III, and IV deficiency for 7 neonates, and combined complexes I and IV deficiency for 3 neonates. No neonates had complex IV deficiency. Six neonates had nuclear mutations, and 2 neonates had the mitochondrial DNA 8993T>G mutation.
Oxidative phosphorylation disorders present commonly in the neonatal period. The combination of nonspecific manifestations such as prematurity and intrauterine growth retardation with early postnatal decompensation or poor feeding or vomiting and persistent lactic acidosis should suggest the possibility of an oxidative phosphorylation disorder.
Leigh syndrome (also termed subacute, necrotizing encephalopathy) is a devastating neurodegenerative disorder, characterized by almost identical brain changes, e.g., focal, bilaterally symmetric lesions, particularly in the basal ganglia, thalamus, and brainstem, but with considerable clinical and genetic heterogeneity. Clinically, Leigh syndrome is characterized by a wide variety of abnormalities, from severe neurologic problems to a near absence of abnormalities. Most frequently the central nervous system is affected, with psychomotor retardation, seizures, nystagmus, ophthalmoparesis, optic atrophy, ataxia, dystonia, or respiratory failure. Some patients also present with peripheral nervous system involvement, including polyneuropathy or myopathy, or non-neurologic abnormalities, e.g., diabetes, short stature, hypertrichosis, cardiomyopathy, anemia, renal failure, vomiting, or diarrhea (Leigh-like syndrome). In the majority of cases, onset is in early childhood, but in a small number of cases, adults are affected. In the majority of cases, dysfunction of the respiratory chain (particularly complexes I, II, IV, or V), of coenzyme Q, or of the pyruvate dehydrogenase complex are responsible for the disease. Associated mutations affect genes of the mitochondrial or nuclear genome. Leigh syndrome and Leigh-like syndrome are the mitochondrial disorders with the largest genetic heterogeneity.
Argininosuccinic acid (A.S.A.) contains the two waste nitrogen atoms later excreted in urea in healthy people, and it has a renal clearance similar to the glomerular filtration-rate. Therefore, argininosuccinic acid might provide a vehicle for the excretion of waste nigrogen in patients with argininosuccinase deficiency, providing that stoichiometric amounts of ornithine are available. When two infants with no, or very little, erythrocyte argininosuccinase activity who were in neonatal hyperammonaemic coma were treated with supplementary arginine (4-5 mmol/kg/day) plasma ammonium, glutamine, and alanine concentrations became normal. One infant grew and developed normally during the first month of life on a protein intake of 2 g/kg/day. The other infant had sustained lathal brain damage before arginine therapy was tried and she died aged 17 days. Arginine supplementation may be effective therapy for argininosuccinase deficiency because it promotes A.S.A. synthesis and hence excretion of waste nitrogen. The effects of high plasma-A.S.A. concentrations are unknown.
The defect in nitrogen excretion in patients with inborn errors of urea synthesis can be controlled by exploiting the biosynthetic pathways of readily excretable non-urea metabolites which contain nitrogen derived from ammonium, alanine, glutamate, and glutamine. Two classes of such metabolites are the urea-cycle intermediates--including citrulline, argininosuccinic acid, and arginine--and the aminoacid acylation products--hippuric acid (the glycine conjugate of benzoic acid) and phenylactylglutamine (the glutamine conjugate of phenylactic acid). Thus the urea cycle may serve as a model for the development of excretion pathways of toxic precursors which accumulate in inborn errors of metabolism.
A 10 month old female infant was evaluated for severe lactic acidosis. Clinically she was well nourished and had a substantial amount of adipose tissue despite recurrent episodes of acidosis. Her psychomotor development was retarded, her movements were dystonic and generalized seizures punctuated her course. Metabolic abnormalities included elevated blood concentrations of lactate, pyruvate, beta-hydroxybutyrate, acetoacetate, alanine, proline and glycine, decreased blood concentrations of glutamine, aspartate, valine and citrate, and intermittent elevations of serum cholesterol. A trial on a high-fat diet worsened the clinical condition and intensified the ketoacidosis and hyperalaninemia. Analysis of hepatic tissue obtained by open biopsy revealed increased concentrations of lactate, alanine, acetyl-CoA and other short-chain acyl-CoA esters, and decreased concentrations of oxaloacetate, citrate, alpha-ketoglutarate, malate and aspartate. The blood and tissue metabolic perturbations reflected a deficiency of hepatic pyruvate carboxylase. The apparent Km of hepatic citrate synthase for oxaloacetate was 4.6 micrometer. Calculated tissue oxaloacetate concentrations were 0.50--0.84 micrometer suggesting that tricarboxylic acid cycle activity was severely limited by the decreased availability of this substrate. An iv glucose tolerance test resulted in the paradoxical synthesis of ketone bodies. This observation, coupled with the intermittent hypercholesterolemia and the increased tissue acetyl-CoA concentrations, suggests that pyruvate carboxylase is important in modulating the fractional distribution of intracellular acetyl-CoA between the tricarboxylic acid cycle, the beta-hydroxy-beta-methyl-glutaryl-CoA cycle (and the synthesis of cholesterol and ketone bodies), and fatty acid synthesis. Treatment in future cases might be directed toward increasing tissue concentrations of oxaloacetate.
Subacute necrotizing encephalomyelopathy (SNE) usually appears before the age of 2 years. Variability in its clinical presentation make antemortem diagnosis difficult. The morphologic diagnosis depends on the present of necrotizing lesions with a characteristic distribution within the CNS. We describe a patient with the uncommon adult form of SNE. The pathologic changes are those accepted as diagnostic of the more common infantile SNE, and permit a separation from Wernicke's encephalopathy. In the adult, the disease is thought to be due to a less severe thiamine-related metabolic defect than that of the infantile form. The infrequent clinical recognition in the adult form may be due in part to lack of medical awareness.
The therapeutic efficacy of oral glycine was tested in a 3-year-old girl with isovaleric acidemia. An oral leucine load (25 mg/kg) caused a rise of the blood levels of isovaleric, lactic, and pyruvic acids as well as an increase of urinary excretion of the ketone bodies. These changes did not occur when oral glycine (250 mg/kg) was given with the leucine. Glycine supplementation favored the formation of isovalerylglycine, a nontoxic conjugate of isovaleric acid which is excreted rapidly. Excretion of isovalerylglycine rose threefold when leucine and glycine were administered simultaneously. Chronic glycine therapy was tolerated well and may have prevented one episode of ketoacidosis.
We report on five preterm infants (34 to 36 weeks' gestation) in whom an overwhelming illness developed within the first 48 hours of life. Each had mild respiratory distress that progressed within 48 hours to deep coma requiring ventilatory assistance. Ammonia concentrations in the plasma ranged from 844 to 7640 microgram per deciliter. Four received exchange transfusion and peritoneal dialysis; ammonia values returned to the normal range (less than 150 mug per deciliter) within 72 hours and remained there even after protein challenge. These four subsequently fed and developed normally. The fifth infant died without an attempt to lower plasma ammonia. In this infant (and two of the others) urea-cycle enzymes measured in liver tissue were in the normal range. Transient hyperammonemia of unknown cause may be a relatively common variety of neonatal hyperammonemia; it responds well to prompt diagnosis and aggressive therapy.
Liver transplantation is the only effective treatment for hereditary tyrosinaemia type I (McKusick 276700). We have treated one acute and four subacute-chronic cases with 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione (NTBC), a potent inhibitor of 4-hydroxyphenylpyruvate dioxygenase (EC 1.13.11.27), to prevent the formation of maleylacetoacetate and fumarylacetoacetate and their saturated derivatives. The oral daily dose was 0.1-0.6 mg/kg. The excretion of succinylacetoacetate and succinylacetone decreased from 15-103 mmol/mol creatinine to the detection limit or slightly above (ie, to 20-150 mumol/mol creatinine). The concentration of succinylacetone in plasma decreased from 5.8-43 mumol/l to the detection limit (0.1 mumol/l) over 2-5 months of treatment. The almost complete inhibition of porphobilinogen synthase in erythrocytes was abolished and the excretion of 5-aminolevulinate decreased to within or slightly above the reference range. The concentration of alpha-fetoprotein decreased in four patients to 1.3-7.5% of initially high values over 6-8 months. Improved liver function was reflected by normal concentrations of prothrombin complex and in decreased activities of alkaline phosphatase and gamma-glutamyltransferase in serum. Computed tomography revealed regression of hepatic abnormalities in three patients. One patient developed rickets 6 months before treatment and had excreted high concentrations of markers of tubular dysfunction--after 3 weeks of treatment, this excretion had disappeared. No side-effects were encountered. Inhibition of 4-hydroxyphenylpyruvate dioxygenase may prevent the development of liver cirrhosis and abolish or diminish the risk of liver cancer. Normalisation of porphyrin synthesis will eliminate the risk of porphyric crises. This type of treatment may thus offer an alternative to liver transplantation in hereditary tyrosinaemia.
Hypergalactosaemia was discovered in a newborn girl during routine metabolic screening. Hereditary enzyme deficiency was ruled out. Because hypergalactosaemia persisted, an open ductus venosus Arantii was suspected but remained undetected by conventional two-dimensional ultrasonography. It was demonstrated by combined colour and pulsed wave Doppler sonography. At age 3 years 6 months, the girl developed initial symptoms of portosystemic encephalopathy which progressed and was treated by protein restriction, oral lactulose and flumazenil, with some success. In the absence of enzyme deficiency, hypergalactosaemia in the newborn is an early sign of duct persistence. For the unambiguous diagnosis of an open duct, colour Doppler sonography is the method of choice. Pulsed wave Doppler sonography is recommended for pathophysiological characterisation of the splanchnic venous return.
An 11-month-old girl presented acute episodes of hypoglycaemia and hepatic encephalopathy reminiscent of Reye syndrome and 3-hydroxydicarboxylic aciduria. The patient showed peculiar clinical manifestations of severe sensory-motor neuropathy, pigmentary retinopathy, and cardiomyopathy. She died of cardiac failure. Pathological studies of peripheral nerve showed signs of axonal neuropathy and demyelination. Enzymatic studies in cultured fibroblasts showed a deficiency of mitochondrial long-chain 3-hydroxyacyl-CoA-dehydrogenase. Peripheral nerve involvement and retinal pigmentary degeneration have as yet not been described in patients with proven defects of mitochondrial beta-oxidation.
We have diagnosed type I glutaric aciduria (GA-I) in 14 children from 7 Old Order Amish families in Lancaster County, Pennsylvania. An otherwise rare disorder, GA-I appears to be a common cause of acute encephalopathy and cerebral palsy among the Amish. The natural history of the disease, which was previously unrecognized in this population, is remarkably variable and ranges from acute infantile encephalopathy and sudden death to static extrapyramidal cerebral palsy to normal adult. Ten patients first manifested the disease between 3 and 18 months at the time of an acute infectious illness. Four of these children died in early childhood, also during acute illnesses. However, there has been little progression of the neurological disease after age 5 years in the surviving children and intellect usually has been preserved, even in children with severe spastic paralysis. When well, patients have plasma glutaric acid concentrations ranging from 4.8 to 14.2 mumol/liter (nl 0-5.6 mumol/liter) and urinary glutaric acid concentrations from 12.5 to 196 mg/g creatinine (nl 0.5-8.4 mg/g creatinine). We have found that GA-I can be diagnosed in the Amish by measurement of urinary glutaric acid concentrations using isotope-dilution gas chromatography/mass spectrometry, whereas the diagnosis can easily be missed by routine urine organic acid gas chromatography.(ABSTRACT TRUNCATED AT 250 WORDS)
Continuous venovenous hemofiltration was used to treat two neonates, one with maple syrup urine disease and the other with an inborn error of long-chain fatty acid oxidation. The latter infant had hypoglycemia, hyperammonemia and lactic acidosis. In both cases, acceptable biochemical control was achieved within 8 hours. This therapy offers the potential to overcome acute crises rapidly in a wide range of inborn errors of intermediary metabolism.