Variable clinical presentation in patients with defective E1 component of pyruvate dehydrogenase complex

Characteristic Fetal Brain MRI Abnormalities in Pyruvate Dehydrogenase Complex Deficiency

Pyruvate dehydrogenase complex deficiency (PDCD) is a disorder of mitochondrial metabolism that is caused by pathogenic variants in multiple genes, including PDHA1. Typical neonatal brain imaging findings in PDCD have been described, with a focus on malformative features and chronic encephaloclastic changes. However, fetal brain MRI imaging in confirmed PDCD has not been comprehensively described. We sought to demonstrate the prenatal neurological and systemic manifestations of PDCD determined by comprehensive fetal imaging and genomic sequencing. All fetuses with a diagnosis of genetic PDCD who had undergone fetal MRI were included in the study. Medical records, imaging data, and genetic testing results were reviewed and reported descriptively. Ten patients with diagnosis of PDCD were included. Most patients had corpus callosum dysgenesis, abnormal gyration pattern, reduced brain volumes, and periventricular cystic lesions. One patient had associated intraventricular hemorrhages. One patient had a midbrain malformation with aqueductal stenosis and severe hydrocephalus. Fetuses imaged in the second trimester were found to have enlargement of the ganglionic eminences with cystic cavitations, while those imaged in the third trimester had germinolytic cysts. Fetuses with PDCD have similar brain MRI findings to neonates described in the literature, although some of these findings may be subtle early in pregnancy. Additional features, such as cystic cavitations of the ganglionic eminences, are noted in the second trimester in fetuses with PDCD, and these may represent a novel early diagnostic marker for PDCD. Using fetal MRI to identify these radiological hallmarks to inform prenatal diagnosis of PDCD may guide genetic counseling, pregnancy decision-making, and neonatal care planning.

Manifestations of X-linked pyruvate dehydrogenase complex deficiency in female PDHA1 carriers

BACKGROUND AND PURPOSE

Pyruvate dehydrogenase complex deficiency is in up to 90% caused by pathogenic variants in the X-linked PDHA1 gene. We aimed to investigate female relatives of index patients with PDHA1-related disease to (i) describe the prevalence of female PDHA1 carriers, (ii) determine whether they had symptoms and signs, and (iii) delineate the associated phenotype.

METHODS

In a national population-based study, we identified 37 patients with pathogenic variants in PDHA1. Sanger sequencing for the presence of the pathogenic variant was performed in their mothers and female relatives. The identified female carriers were clinically assessed, and their medical records were reviewed.

RESULTS

The proportion carrying a de novo variant was 86%. We identified seven female PDHA1 carriers from five families. Five of them exhibited clinical features of the disease and were previously undiagnosed; all had signs of peripheral axonal neuropathy, four presented with strokelike episodes including two with Leigh-like lesions, and three had facial stigmata.

CONCLUSIONS

PDHA1-related disease is underrecognized in heterozygous female carriers. Peripheral axonal neuropathy, strokelike and Leigh-like changes, and facial dysmorphism should raise suspicion of the disorder. Genetic analysis and clinical examination of potential female carriers are important for genetic counseling and have implications for treatment.

Inborn Errors of Metabolism with Ataxia: Current and Future Treatment Options

A number of hereditary ataxias are caused by inborn errors of metabolism (IEM), most of which are highly heterogeneous in their clinical presentation. Prompt diagnosis is important because disease-specific therapies may be available. In this review, we offer a comprehensive overview of metabolic ataxias summarized by disease, highlighting novel clinical trials and emerging therapies with a particular emphasis on first-in-human gene therapies. We present disease-specific treatments if they exist and review the current evidence for symptomatic treatments of these highly heterogeneous diseases (where cerebellar ataxia is part of their phenotype) that aim to improve the disease burden and enhance quality of life. In general, a multimodal and holistic approach to the treatment of cerebellar ataxia, irrespective of etiology, is necessary to offer the best medical care. Physical therapy and speech and occupational therapy are obligatory. Genetic counseling is essential for making informed decisions about family planning.

Recurrent Sensory-Motor Neuropathy Mimicking CIDP as Predominant Presentation of PDH Deficiency

INTRODUCTION

 Pyruvate dehydrogenase complex (PDH) deficiency (Online Mendelian Inheritance in Man # 312170) is a relatively common mitochondrial disorder, caused by mutations in the X-linked PDHA1 gene and presenting with a variable phenotypic spectrum, ranging from severe infantile encephalopathy to milder chronic neurological disorders.Isolated peripheral neuropathy as predominant clinical presentation is uncommon.

RESULTS

 We report on a patient, now 21 years old, presenting at the age of 2 years with recurrent symmetric weakness as first symptom of a PDH deficiency. Neurophysiological evaluation proving a sensory-motor polyneuropathy with conduction blocks and presence of elevated cerebrospinal fluid proteins, suggested a chronic inflammatory demyelinating polyneuropathy. The evidence of high serum lactate and the alterations in oxidative metabolism in muscle biopsy pointed toward the final diagnosis. After starting nutritional supplements, no further episodes occurred. A hemizygous mutation in PDHA1 (p.Arg88Cys) was identified. This mutation has been previously described in five patients with a similar phenotype. A three-dimensional reconstruction demonstrated that mutations affecting this arginine destabilize the interactions between the subunits of the E1 complex.

CONCLUSION

 We summarize the clinical and genetic characteristics of one patient with PDH deficiency presenting isolated peripheral nervous system involvement. This study highlights that the diagnosis of PDH deficiency should be considered in children with unexplained peripheral neuropathy, even with features suggestive of acquired forms, especially in case of early onset and limited response to treatment. A simple analysis of lactic acid could help to target the diagnosis.In addition, we suggest that the residue Arg88 is the most frequently involved in this specific phenotype of PDH deficiency.

The pyruvate dehydrogenase complex: Life's essential, vulnerable and druggable energy homeostat

Found in all organisms, pyruvate dehydrogenase complexes (PDC) are the keystones of prokaryotic and eukaryotic energy metabolism. In eukaryotic organisms these multi-component megacomplexes provide a crucial mechanistic link between cytoplasmic glycolysis and the mitochondrial tricarboxylic acid (TCA) cycle. As a consequence, PDCs also influence the metabolism of branched chain amino acids, lipids and, ultimately, oxidative phosphorylation (OXPHOS). PDC activity is an essential determinant of the metabolic and bioenergetic flexibility of metazoan organisms in adapting to changes in development, nutrient availability and various stresses that challenge maintenance of homeostasis. This canonical role of the PDC has been extensively probed over the past decades by multidisciplinary investigations into its causal association with diverse physiological and pathological conditions, the latter making the PDC an increasingly viable therapeutic target. Here we review the biology of the remarkable PDC and its emerging importance in the pathobiology and treatment of diverse congenital and acquired disorders of metabolic integration.

Metabolic fingerprinting of dogs with idiopathic epilepsy receiving a ketogenic medium-chain triglyceride (MCT) oil

Consumption of medium-chain triglycerides (MCT) has been shown to improve seizure control, reduce behavioural comorbidities and improve cognitive function in epileptic dogs. However, the exact metabolic pathways affected by dietary MCT remain poorly understood. In this study, we aimed to identify changes in the metabolome and neurotransmitters levels relevant to epilepsy and behavioural comorbidities associated with the consuming of an MCT supplement (MCT-DS) in dogs with idiopathic epilepsy (IE). Metabolic alterations induced by a commercial MCT-DS in a population of 28 dogs with IE were evaluated in a 6-month multi-centre, prospective, randomised, double-blinded, controlled cross-over trial design. A metabolic energy requirement-based amount of 9% MCT or control oil was supplemented to the dogs' stable base diet for 3 months, followed by the alternative oil for another 3 months. A validated, quantitative nuclear magnetic resonance (NMR) spectroscopy platform was applied to pre- and postprandially collected serum samples to compare the metabolic profile between both DS and baseline. Furthermore, alterations in urinary neurotransmitter levels were explored. Five dogs (30%) had an overall reduction in seizure frequency of ≥50%, and were classified as MCT-responders, while 23 dogs showed a ≤50% reduction, and were defined as MCT non-responders. Amino-acid metabolism was significantly influenced by MCT consumption compared to the control oil. While the serum concentrations of total fatty acids appeared similar during both supplements, the relative concentrations of individual fatty acids differed. During MCT supplementation, the concentrations of polyunsaturated fatty acids and arachidonic acid were significantly higher than under the control oil. β-Hydroxybutyric acid levels were significantly higher under MCT supplementation. In total, four out of nine neurotransmitters were significantly altered: a significantly increased γ-aminobutyric acid (GABA) concentration was detected during the MCT-phase accompanied by a significant shift of the GABA-glutamate balance. MCT-Responders had significantly lowered urinary concentrations of histamine, glutamate, and serotonin under MCT consumption. In conclusion, these novel data highlight metabolic changes in lipid, amino-acid and ketone metabolism due to MCT supplementation. Understanding the metabolic response to MCT provides new avenues to develop better nutritional management with improved anti-seizure and neuroprotective effects for dogs with epilepsy, and other behavioural disorders.

Solvent accessibility of E1α and E1β residues with known missense mutations causing pyruvate dehydrogenase complex (PDC) deficiency: Impact on PDC-E1 structure and function

Pyruvate dehydrogenase complex deficiency is a major cause of primary lactic acidemia resulting in high morbidity and mortality, with limited therapeutic options. PDHA1 mutations are responsible for >82% of cases. The E1 component of PDC is a symmetric dimer of heterodimers (αβ/α'β') encoded by PDHA1 and PDHB. We measured solvent accessibility surface area (SASA), utilized nearest-neighbor analysis, incorporated sequence changes using mutagenesis tool in PyMOL, and performed molecular modeling with SWISS-MODEL, to investigate the impact of residues with disease-causing missense variants (DMVs) on E1 structure and function. We reviewed 166 and 13 genetically resolved cases due to PDHA1 and PDHB, respectively, from variant databases. We expanded on 102 E1α and 13 E1β nonduplicate DMVs. DMVs of E1α Arg112-Arg224 stretch (exons 5-7) and of E1α Arg residues constituted 40% and 39% of cases, respectively, with invariant Arg349 accounting for 22% of arginine replacements. SASA analysis showed that 86% and 84% of residues with nonduplicate DMVs of E1α and E1β, respectively, are solvent inaccessible ("buried"). Furthermore, 30% of E1α buried residues with DMVs are deleterious through perturbation of subunit-subunit interface contact (SSIC), with 73% located in the Arg112-Arg224 stretch. E1α Arg349 represented 74% of buried E1α Arg residues involved in SSIC. Structural perturbations resulting from residue replacements in some matched neighboring pairs of amino acids on different subunits involved in SSIC at 2.9-4.0 Å interatomic distance apart, exhibit similar clinical phenotype. Collectively, this work provides insight for future target-based advanced molecular modeling studies, with implications for development of novel therapeutics for specific recurrent DMVs of E1α.

Novel imaging findings in pyruvate dehydrogenase complex (PDHc) deficiency-Results from a nationwide population-based study

The vast clinical and radiological spectrum of pyruvate dehydrogenase complex (PDHc) deficiency continues to pose challenges both in diagnostics and disease monitoring. Prompt diagnosis is important to enable early initiation of ketogenic diet. The patients were recruited from an ongoing population-based study in Sweden. All patients with a genetically confirmed diagnosis who had been investigated with an MRI of the brain were included. Repeated investigations were assessed to study the evolution of the MRI changes. Sixty-two MRI investigations had been performed in 34 patients (23 females). The genetic cause was mutations in PDHA1 in 29, PDHX and DLAT in 2 each, and PDHB in 1. The lesions were prenatal developmental in 16, prenatal clastic in 18, and postnatal clastic in 15 individuals. Leigh-like lesions with predominant involvement of globus pallidus were present in 12, while leukoencephalopathy was present in 6 and stroke-like lesions in 3 individuals. A combination of prenatal developmental and clastic lesions was present in 15 individuals. In addition, one male with PDHA1 also had postnatal clastic lesions. The most common lesions found in our study were agenesis or hypoplasia of corpus callosum, ventriculomegaly, or Leigh-like lesions. Furthermore, we describe a broad spectrum of other MRI changes that include leukoencephalopathy and stroke-like lesions. We argue that a novel important clue, suggesting the possibility of PDHc deficiency on MRI scans, is the simultaneous presence of multiple lesions on MRI that have occurred during different phases of brain development.

Novel presentations associated with a PDHA1 variant - Alternating hemiplegia in Hemizygote proband and Guillain Barre Syndrome in Heterozygote mother

We report a 5-year-old male with a PDHA1 variant who presented with alternating hemiplegia of childhood and later developed developmental regression, basal ganglia injury and episodic lactic acidosis. Enzyme assay in lymphocytes confirmed a diagnosis of Pyruvate Dehydrogenase Complex (PDC) deficiency. His mother who was heterozygous for the same variant suffered from ophthalmoplegia, chronic migraine and developed flaccid paralysis at 36 years of age. PDHA1 is the most common genetic cause of PDC deficiency and presents with a myriad of neurological phenotypes including neonatal form with lactic acidosis, non-progressive infantile encephalopathy, Leigh syndrome subtype and intermittent ataxia. The presentations in our 2 patients contribute to the clinical heterogeneity of this neurogenetic condition.

Utility of specific amino acid ratios in screening for pyruvate dehydrogenase complex deficiencies and other mitochondrial disorders associated with congenital lactic acidosis and newborn screening prospects

Pyruvate dehydrogenase complex deficiencies (PDCDs) and other mitochondrial disorders (MtDs) can (a) result in congenital lactic acidosis with elevations of blood alanine (Ala) and proline (Pro), (b) lead to decreased ATP production, and (c) result in high morbidity and mortality. With ~140,000 live births annually in Ohio and ~1 in 9,000 overall prevalence of MtDs, we estimate 2 to 3 newborns will have PDCD and 13 to 14 others likely will have another MtD annually. We compared the sensitivities of plasma amino acids (AA) Alanine (Ala), Alanine:Leucine (Ala:Leu), Alanine:Lysine and the combination of Ala:Leu and Proline:Leucine (Pro:Leu), in subjects with known primary-specific PDCD due to PDHA1 and PDHB mutations vs controls. Furthermore, in collaboration with the Ohio newborn screening (NBS) laboratory, we determined Ala and Pro concentrations in dried blood spot (DBS) specimens using existing NBS analytic approaches and evaluated Ala:Leu and Pro:Leu ratios from DBS specimens of 123,414 Ohio newborns in a 12-month period. We used the combined Ala:Leu ≥4.0 and Pro:Leu ≥3.0 ratio criterion from both DBS and plasma specimens as a screening tool in our retrospective review of newborn data. The screening tool applied on DBS and/or plasma (or serum) AA specimens successfully identified three unrelated females with novel de novo PDHA1 mutations, one male with a novel de novo X-linked HSD17B10 mutation, and a female with VARS2 mutations. This work lays the first step for piloting an NBS protocol in Ohio for identifying newborns at high risk for primary-specific PDCD and other MtDs who might benefit from neonatal diagnosis and early institution of known therapy and/or potential novel therapies for such disorders.

A novel null mutation in the pyruvate dehydrogenase phosphatase catalytic subunit gene (PDP1) causing pyruvate dehydrogenase complex deficiency

Congenital lactic acidosis due to pyruvate dehydrogenase phosphatase (PDP) deficiency is very rare. PDP regulates pyruvate dehydrogenase complex (PDC) and defective PDP leads to PDC deficiency. We report a case with functional PDC deficiency with low activated (+dichloroacetate) and inactivated (+fluoride) PDC activities in lymphocytes and fibroblasts, normal activity of other mitochondrial enzymes in fibroblasts, and novel biallelic frameshift mutation in the PDP1 gene, c.575dupT (p.L192FfsX5), with absent PDP1 product in fibroblasts. Unexpectedly, the patient also had low branched-chain 2-ketoacid dehydrogenase (BCKDH) activity in fibroblasts with slight elevation of branched-chain amino acids in plasma and ketoacids in urine but with no pathogenic mutations in the enzymes of BCKDH, which could suggest shared regulatory function of PDC and BCKDH in fibroblasts, potentially in other tissues or cell types as well, but this remains to be determined. The clinical presentation of this patient overlaps that of other patients with primary-specific PDC deficiency, with neonatal/infantile and childhood lactic acidosis, normal lactate to pyruvate ratio, elevated plasma alanine, delayed psychomotor development, epileptic encephalopathy, feeding difficulties, and hypotonia. This patient exhibited marked improvement of overall development following initiation of ketogenic diet at 31 months of age. To the best of our knowledge, this is the fourth case of functional PDC deficiency with a defined mutation in PDP1.

SYNOPSIS

Pyruvate dehydrogenase phosphatase (PDP) regulates pyruvate dehydrogenase complex (PDC) and defective PDP due to PDP1 mutations leads to PDC deficiency and congenital lactic acidosis.

Metabolic etiologies in West syndrome

West syndrome (WS) is an early life epileptic encephalopathy associated with infantile spasms, interictal electroencephalography (EEG) abnormalities including high amplitude, disorganized background with multifocal epileptic spikes (hypsarrhythmia), and often neurodevelopmental impairments. Approximately 64% of the patients have structural, metabolic, genetic, or infectious etiologies and, in the rest, the etiology is unknown. Here we review the contribution of etiologies due to various metabolic disorders in the pathology of WS. These may include metabolic errors in organic molecules involved in amino acid and glucose metabolism, fatty acid oxidation, metal metabolism, pyridoxine deficiency or dependency, or acidurias in organelles such as mitochondria and lysosomes. We discuss the biochemical, clinical, and EEG features of these disorders as well as the evidence of how they may be implicated in the pathogenesis and treatment of WS. The early recognition of these etiologies in some cases may permit early interventions that may improve the course of the disease.

Prenatal sonographic description of fetuses affected by pyruvate dehydrogenase or pyruvate carboxylase deficiency

OBJECTIVE

Pyruvate dehydrogenase deficiency (PDHD) and pyruvate carboxylase deficiency (PCD) are diseases with severe neonatal forms, and their low prevalence makes them difficult to diagnose during pregnancy. Our objective was to describe prenatal ultrasound features that may be suggestive of these diagnoses.

METHODS

We analyzed 3 cases from our institution and reviewed 12 published cases of PDHD and 6 cases of PCD, recording all of the ultrasound signs, as well as magnetic resonance findings when available. Because of the small number of cases of PCD, we also included postnatal signs that could have been observed during imaging during pregnancy, for a total of 11 cases of PCD.

RESULTS

We conclude that PDHD can be suggested in the presence of ventriculomegaly or paraventricular cysts, associated with an abnormality of the cerebral parenchyma such as abnormal gyration or involvement of the corpus callosum. Pyruvate carboxylase deficiency can be suggested in the presence of ventriculomegaly, frontal horn impairment associated with subependymal, and paraventricular cysts.

CONCLUSION

When confronted to the ultrasound abnormalities we described, and after eliminating the most frequent etiologies, a metabolic deficiency should be considered. Furthermore, the hereditary character of these diseases makes that it is important to send the family with genetic advice in particular in case of history of a fetal death in utero or a death neonatal unexplained.

Development of a novel observer reported outcome tool as the primary efficacy outcome measure for a rare disease randomized controlled trial

We developed an Observer-Reported Outcome (ObsRO) survey instrument to be applied in a multicenter, placebo-controlled, crossover randomized controlled trial of dichloroacetate in children with pyruvate dehydrogenase complex deficiency. The instrument quantifies a subject's at-home level of functionality, as reported by a parent/caregiver, who were instrumental in providing the clinical descriptors and domains that formed the instrument's content. Feasibility testing of the ObsRO tool showed it to be easy to use and comprehensive in capturing the major clinical functional limitations of affected children and requires less than 5min for a parent/caregiver to complete daily.

Clinical manifestations in two patients with pyruvate dehydrogenase deficiency and long-term survival

Pyruvate dehydrogenase E1-alpha deficiency (PDHAD) results in lactic acidosis and hyperpyruvatemia. Two patients with PDHAD, a man with a p.R263Q mutation, and a girl with a p.C145del mutation in PDHE1α, presented with lactic acidosis with neurological disorder. These patients were able to survive for a long period under careful nursing care. Herein, we discuss the factors contributing to their relatively stable clinical course, albeit with intellectual disability.

Prenatal and postnatal presentations of corpus callosum agenesis with polymicrogyria caused by EGP5 mutation

EPG5-related Vici syndrome is a rare multisystem autosomal recessive disorder characterized by corpus callosum agenesis (ACC), hypopigmentation, cataracts, acquired microcephaly, failure to thrive, cardiomyopathy and profound developmental delay, and immunodeficiency. We report here the first case of prenatally diagnosed Vici syndrome with delayed gyration associated with ACC. Trio based exome sequencing allowed the identification of a compound heterozygous mutation in the EPG5 gene. Our patient subsequently demonstrated severe developmental delay, hypopigmentation, progressive microcephaly, and failure to thrive which led to suspicion of the diagnosis. Her MRI demonstrated ACC with frontoparietal polymicrogyria, severe hypomyelination, and pontocerebellar atrophy. This prenatal presentation of malformations of cortical development in combination with ACC expands the EPG5-related phenotypic spectrum. Our report supports the idea that EPG5-related Vici syndrome is both a neurodevelopmental and neurodegenerative disorder. © 2017 Wiley Periodicals, Inc.

Ketogenic diet in pyruvate dehydrogenase complex deficiency: short- and long-term outcomes

OBJECTIVES

Our aime was to study the short- and long-term effects of ketogenic diet on the disease course and disease-related outcomes in patients with pyruvate dehydrogenase complex deficiency, the metabolic factors implicated in treatment outcomes, and potential safety and compliance issues.

METHODS

Pediatric patients diagnosed with pyruvate dehydrogenase complex deficiency in Sweden and treated with ketogenic diet were evaluated. Study assessments at specific time points included developmental and neurocognitive testing, patient log books, and investigator and parental questionnaires. A systematic literature review was also performed.

RESULTS

Nineteen patients were assessed, the majority having prenatal disease onset. Patients were treated with ketogenic diet for a median of 2.9 years. All patients alive at the time of data registration at a median age of 6 years. The treatment had a positive effect mainly in the areas of epilepsy, ataxia, sleep disturbance, speech/language development, social functioning, and frequency of hospitalizations. It was also safe-except in one patient who discontinued because of acute pancreatitis. The median plasma concentration of ketone bodies (3-hydroxybutyric acid) was 3.3 mmol/l. Poor dietary compliance was associated with relapsing ataxia and stagnation of motor and neurocognitive development. Results of neurocognitive testing are reported for 12 of 19 patients.

CONCLUSION

Ketogenic diet was an effective and safe treatment for the majority of patients. Treatment effect was mainly determined by disease phenotype and attainment and maintenance of ketosis.

Phenotypic and Neuropathological Characterization of Fetal Pyruvate Dehydrogenase Deficiency

To distinguish pyruvate dehydrogenase deficiency (PDH) from other antenatal neurometabolic disorders thereby improving prenatal diagnosis, we describe imaging findings, clinical phenotype, and brain lesions in fetuses from 3 families with molecular characterization of this condition. Neuropathological analysis was performed in 4 autopsy cases from 3 unrelated families with subsequent biochemical and molecular confirmation of PDH complex deficiency. In 2 families there were mutations in the PDHA1 gene; in the third family there was a mutation in the PDHB gene. All fetuses displayed characteristic craniofacial dysmorphism of varying severity, absence of visceral lesions, and associated encephaloclastic and developmental supra- and infratentorial lesions. Neurodevelopmental abnormalities included microcephaly, migration abnormalities (pachygyria, polymicrogyria, periventricular nodular heterotopias), and cerebellar and brainstem hypoplasia with hypoplastic dentate nuclei and pyramidal tracts. Associated clastic lesions included asymmetric leukomalacia, reactive gliosis, large pseudocysts of germinolysis, and basal ganglia calcifications. The diagnosis of PDH deficiency should be suspected antenatally with the presence of clastic and neurodevelopmental lesions and a relatively characteristic craniofacial dysmorphism. Postmortem examination is essential for excluding other closely related entities, thereby allowing for biochemical and molecular confirmation.

Key proteins of activating cell death can be predicted through a kainic acid-induced excitotoxic stress

Epilepsy is a major neurological disorder characterized by spontaneous seizures accompanied by neurophysiological changes. Repeated seizures can damage the brain as neuronal death occurs. A better understanding of the mechanisms of brain cell death could facilitate the discovery of novel treatments for neurological disorders such as epilepsy. In this study, a model of kainic acid- (KA-) induced neuronal death was established to investigate the early protein markers associated with apoptotic cell death due to excitotoxic damage in the rat cortex. The results indicated that KA induces both apoptotic and necrotic cell death in the cortex. Incubation with high concentrations (5 and 500 μM, >75%) and low concentrations (0.5 pM: 95% and 50 nM: 8%) of KA for 180 min led to necrotic and apoptotic cell death, respectively. Moreover, proteomic analysis using two-dimensional gel electrophoresis and mass spectrometry demonstrated that antiapoptotic proteins, including heat shock protein 70, 3-mercaptopyruvate sulfurtransferase, tubulin-B-5, and pyruvate dehydrogenase E1 component subunit beta, were significantly higher in apoptosis than in necrosis induced by KA. Our findings provide direct evidence that several proteins are associated with apoptotic and necrotic cell death in excitotoxicity model. The results indicate that these proteins can be apoptotic biomarkers from the early stages of cell death.

Hereditary neurometabolic causes of infantile spasms in 80 children presenting to a tertiary care center

BACKGROUND

Infantile spasms are a devastating infantile epileptic syndrome with multiple etiologies. Hereditary neurometabolic disorders are rarely recognized causes of infantile spasms. The aim of this study was to identify hereditary neurometabolic disorders when they were the cause of infantile spasms in patients presenting to a tertiary care center in Saudi Arabia.

METHODOLOGY

We conducted a retrospective review of children presenting to the Pediatric Department of King Abdulaziz Medical City in Riyadh, Saudi Arabia over a 15-year interval.

RESULTS

Eighty patients with infantile spasms were identified. A hereditary neurometabolic disorder was diagnosed in 10 patients (12.5%). Of these patients, two had a Leigh-like disorder and one patient had each of the following diagnoses: ethylmalonic aciduria, nonketotic hyperglycinemia, hyperinsulinemic hypoglycemia, leukodystrophy, short-chain acyl-coenzyme A dehydrogenase deficiency, molybdenum cofactor deficiency, primary carnitine deficiency, and neonatal hypoglycemia due to panhypopituitarism. This article is the first to report the association of the last three conditions with infantile spasms. Compared with the other etiologies, the hereditary neurometabolic disorder group had a strong history of similar disease in the same family (P = 0.002), and most of the patients were born of consanguineous parents (P = 0.021). In addition, a typical hypsarrhythmia pattern was more common in the hereditary neurometabolic disorder group (P = 0.003). Furthermore, this group had a poor response to therapy (P = 0.04). Otherwise, there were no significant differences regarding the type of spasms, neuroimaging or outcome; however, there was a trend toward poorer outcomes and death in the hereditary neurometabolic disorder group.

CONCLUSION

Hereditary neurometabolic disorders are relatively common causes of infantile spasms in this subpopulation of Saudi patients. An early diagnosis via proper metabolic and genetic testing has significant implications for applying specific treatments and for facilitating proper family counseling.

Founder p.Arg 446* mutation in the PDHX gene explains over half of cases with congenital lactic acidosis in Roma children

Investigation of 31 of Roma patients with congenital lactic acidosis (CLA) from Bulgaria identified homozygosity for the R446* mutation in the PDHX gene as the most common cause of the disorder in this ethnic group. It accounted for around 60% of patients in the study and over 25% of all CLA cases referred to the National Genetic Laboratory in Bulgaria. The detection of a homozygous patient from Hungary and carriers among population controls from Romania and Slovakia suggests a wide spread of the mutation in the European Roma population. The clinical phenotype of the twenty R446* homozygotes was relatively homogeneous, with lactic acidosis crisis in the first days or months of life as the most common initial presentation (15/20 patients) and delayed psychomotor development and/or seizures in infancy as the leading manifestations in a smaller group (5/20 patients). The subsequent clinical picture was dominated by impaired physical growth and a very consistent pattern of static cerebral palsy-like encephalopathy with spasticity and severe to profound mental retardation seen in over 80% of cases. Most patients had a positive family history. We propose testing for the R446* mutation in PDHX as a rapid first screening in Roma infants with metabolic acidosis. It will facilitate and accelerate diagnosis in a large proportion of cases, allow early rehabilitation to alleviate the chronic clinical course, and prevent further affected births in high-risk families.

Thiamine-Responsive and Non-responsive Patients with PDHC-E1 Deficiency: A Retrospective Assessment

Pyruvate dehydrogenase complex (PDHC) deficiency is a disorder of energy metabolism that leads to a range of clinical manifestations. We sought to characterise clinical manifestations and biochemical, neuroimaging and molecular findings in thiamine-responsive and nonresponsive PDHC-deficient patients and to identify potential pitfalls in the diagnosis of PDHC deficiency. We retrospectively reviewed all medical records of all PDHC-deficient patients (n = 19; all had PDHA1 gene mutations) and one patient with severe PDHC deficiency secondary to 3-hydroxyisobutyryl-CoA hydrolase deficiency managed at our centre between 1982 and 2012. Responsiveness to thiamine was based on clinical parameters. Seventeen patients received thiamine treatment: eight did not respond, four showed sustained response and the others responded temporarily/questionably. Sustained response was noted at thiamine doses >400 mg/day. Age at presentation was 0-6 and 12-27 months in the nonresponsive (n = 8) and responsive (n = 4) patients, respectively. Corpus callosum abnormalities were noted in 4/8 nonresponsive patients. Basal ganglia involvement (consistent with Leigh disease) was found in four patients (including 2/4 thiamine-responsive patients). Diagnosis through mutation analysis was more sensitive and specific than through enzymatic analysis. We conclude that patients presenting at age >12 months with relapsing ataxia and possibly Leigh syndrome are more likely to be thiamine responsive than those presenting with neonatal lactic acidosis and corpus callosum abnormalities. However, this distinction is equivocal and treatment with thiamine (>400 mg/day) should be commenced on all patients suspected of having PDHC deficiency. Mutation analysis is the preferable first-line diagnostic test to avoid missing thiamine-responsive patients and misdiagnosing patients with secondary PDHC deficiency.

SHORT SUMMARY

Thiamine responsiveness is more likely in patients presenting at age >12 months with relapsing ataxia and possibly Leigh syndrome than in those presenting with neonatal lactic acidosis and corpus callosum abnormalities. Thiamine doses >400 mg/day are required for sustained response. Mutation analysis is more sensitive and specific than enzymatic analysis as a first-line diagnostic test.

Cerebral Developmental Abnormalities in a Mouse with Systemic Pyruvate Dehydrogenase Deficiency

Pyruvate dehydrogenase (PDH) complex (PDC) deficiency is an inborn error of pyruvate metabolism causing a variety of neurologic manifestations. Systematic analyses of development of affected brain structures and the cellular processes responsible for their impairment have not been performed due to the lack of an animal model for PDC deficiency. METHODS: In the present study we investigated a murine model of systemic PDC deficiency by interrupting the X-linked Pdha1 gene encoding the α subunit of PDH to study its role on brain development and behavioral studies. RESULTS: Male embryos died prenatally but heterozygous females were born. PDC activity was reduced in the brain and other tissues in female progeny compared to age-matched control females. Immunohistochemical analysis of several brain regions showed that approximately 40% of cells were PDH⁻. The oxidation of glucose to CO₂ and incorporation of glucose-carbon into fatty acids were reduced in brain slices from 15 day-old PDC-deficient females. Histological analyses showed alterations in several structures in white and gray matters in 35 day-old PDC-deficient females. Reduction in total cell number and reduced dendritic arbors in Purkinje neurons were observed in PDC-deficient females. Furthermore, cell proliferation, migration and differentiation into neurons by newly generated cells were reduced in the affected females during pre- and postnatal periods. PDC-deficient mice had normal locomotor activity in a novel environment but displayed decreased startle responses to loud noises and there was evidence of abnormal pre-pulse inhibition of the startle reflex. CONCLUSIONS: The results show that a reduction in glucose metabolism resulting in deficit in energy production and fatty acid biosynthesis impairs cellular differentiation and brain development in PDC-deficient mice.

Two Japanese patients with Leigh syndrome caused by novel SURF1 mutations

We report two patients with Leigh syndrome that showed a combination of facial dysmorphism and MRI imaging indicating an SURF1 deficiency, which was confirmed by sequence analysis. Case 1 is a 3-year-old girl with failure to thrive and developmental delay. She presented with tachypnea at rest and displayed facial dysmorphism including frontal bossing, lateral displacement of inner canthi, esotropia, maxillary hypoplasia, slightly upturned nostril, and hypertrichosis dominant on the forehead and extremities. Case 2 is an 8-year-old boy with respiratory failure. He had been diagnosed as selective complex IV deficiency. Case 2 displayed facial dysmorphism and hypertrichosis. Since both patients displayed characteristic facial dysmorphism and MRI findings, we sequenced the SURF1 gene and identified two heterozygous mutations; c.49+1 G>T and c.752_753del in Case 1, and homozygous c.743 C>A in Case 2. For patients with Leigh syndrome showing these facial dysmorphism and hypertrichosis, sequence analysis of the SURF1 gene may be useful.

Spectrum of neurological and survival outcomes in pyruvate dehydrogenase complex (PDC) deficiency: lack of correlation with genotype

Pyruvate dehydrogenase complex (PDC) deficiency is a relatively common mitochondrial disorder that primarily presents with neurological manifestations and lactic acidemia. We analyzed the clinical outcomes and neurological features of 59 consented symptomatic subjects (27 M, 32 F), who were confirmed to have PDC deficiency with defined mutations in one of the genes of PDC (PDHA1, n = 53; PDHB, n = 4; DLAT, n = 2), including 47 different mutations, of which 22 were novel, and for whom clinical records and/or structured interviews were obtained. 39% of these subjects (23/59) have died. Of these, 91% (21/23) died before age 4 years, 61% (14/23) before 1 year, and 43% (10/23) before 3 months. 56% of males died compared with 25% of females. Causes of death included severe lactic acidosis, respiratory failure, and infection. In subjects surviving past 6 months, a broad range of intellectual outcomes was observed. Of 42 subjects whose intellectual abilities were professionally evaluated, 19% had normal or borderline intellectual ability (CQ/IQ ≥ 70), 10% had mild intellectual disability (ID) (CQ/IQ 55-69), 17% had moderate ID (CQ/IQ 40-54), 24% had severe ID (CQ/IQ 25-39) and 33% had profound ID (CQ/IQ<25). Assessment by parents was comparable. Of 10 subjects who reached age 12 years, 9 had had professional IQ assessments, and only 4 had IQs ≥ 70 (only 2 of these 4 had assessments after age 12 years). The average outcome for females was severe-to-profound ID, whereas that of males was mild-to-moderate ID. Of subjects for whom specific neurological data were available, the majority had hypotonia (89%), and hypertonia or mixed hyper-/hypotonia (49%) were common. Seizures (57%), microcephaly (49%), and structural brain abnormalities including ventriculomegaly (67%) and agenesis, dysgenesis, or hypoplasia of the corpus callosum (55%) were common. Leigh syndrome was found in only 35%. Structural brain abnormalities were more common in females, and Leigh syndrome was more common in males. In a subgroup of 16 ambulatory subjects >3.5 years in whom balance was evaluated, ataxia was found in 13. Peripheral neuropathy was documented in 2 cases but not objectively evaluated in most subjects. Outcomes of this population with genetically confirmed PDC deficiency are heterogeneous and not distinctive. Correlations between specific genotypes and outcomes were not established. Although more females survive, related to the prevalence of X-linked PDHA1 mutations, symptomatic surviving females are generally more severely impaired cognitively and have a different pattern of neurological impairment compared to males. Neonatal or infant onset of symptoms was associated with poor outcomes. Males with PDHA1 mutations and low fibroblast PDC activity were less likely to survive beyond infancy. Recurrence rate in siblings of subjects with PDHA1 mutation was less than 5%. Paradoxically, in this retrospective review, potential factors considered possibly relevant to development, such as in vitro PDC activity, specific mutations, use of ketogenic diets, supplements, or medications, were generally not confirmed to be significantly correlated with objective outcomes of survival or neuro-cognitive function. Therefore, the basis of variability of these outcomes remains largely undetermined.

Infantile spasms (West syndrome) in children with inborn errors of metabolism: a review of the literature

West syndrome (infantile spasms) is an epileptic encephalopathy that includes psychomotor deterioration. In rare cases, it is due to an inherited, progressive metabolic disease. More than 25 inborn errors of metabolism have been considered etiologic or predisposing factors for infantile spasms. This is a review of the literature on reported cases of children diagnosed with a metabolic disease who developed infantile spasms. This article presents in brief the most frequent inborn errors of metabolism that have been associated with West syndrome and also illustrates the importance of screening for inborn errors of metabolism in infantile spasms.

The spectrum of pyruvate dehydrogenase complex deficiency: clinical, biochemical and genetic features in 371 patients

CONTEXT

Pyruvate dehydrogenase complex (PDC) deficiency is a genetic mitochondrial disorder commonly associated with lactic acidosis, progressive neurological and neuromuscular degeneration and, usually, death during childhood. There has been no recent comprehensive analysis of the natural history and clinical course of this disease.

OBJECTIVE

We reviewed 371 cases of PDC deficiency, published between 1970 and 2010, that involved defects in subunits E1α and E1β and components E1, E2, E3 and the E3 binding protein of the complex.

DATA SOURCES AND EXTRACTION

English language peer-reviewed publications were identified, primarily by using PubMed and Google Scholar search engines.

RESULTS

Neurodevelopmental delay and hypotonia were the commonest clinical signs of PDC deficiency. Structural brain abnormalities frequently included ventriculomegaly, dysgenesis of the corpus callosum and neuroimaging findings typical of Leigh syndrome. Neither gender nor any clinical or neuroimaging feature differentiated the various biochemical etiologies of the disease. Patients who died were younger, presented clinically earlier and had higher blood lactate levels and lower residual enzyme activities than subjects who were still alive at the time of reporting. Survival bore no relationship to the underlying biochemical or genetic abnormality or to gender.

CONCLUSIONS

Although the clinical spectrum of PDC deficiency is broad, the dominant clinical phenotype includes presentation during the first year of life; neurological and neuromuscular degeneration; structural lesions revealed by neuroimaging; lactic acidosis and a blood lactate:pyruvate ratio ≤ 20.

Seizures and X-linked intellectual disability

Intellectual disability occurs as an isolated X-linked trait and as a component of recognizable X-linked syndromes in the company of somatic, metabolic, neuromuscular, or behavioral abnormalities. Seizures accompany intellectual disability in almost half of these X-linked disorders. The spectrum of seizures found in the X-linked intellectual disability syndromes is broad, varying in time of onset, type of seizure, and response to anticonvulsant therapy. The majority of the genes associated with XLID and seizures have now been identified.

The spectrum of pyruvate dehydrogenase complex deficiency: clinical, biochemical and genetic features in 371 patients

CONTEXT

Pyruvate dehydrogenase complex (PDC) deficiency is a genetic mitochondrial disorder commonly associated with lactic acidosis, progressive neurological and neuromuscular degeneration and, usually, death during childhood. There has been no recent comprehensive analysis of the natural history and clinical course of this disease.

OBJECTIVE

We reviewed 371 cases of PDC deficiency, published between 1970 and 2010, that involved defects in subunits E1α and E1β and components E1, E2, E3 and the E3 binding protein of the complex.

DATA SOURCES AND EXTRACTION

English language peer-reviewed publications were identified, primarily by using PubMed and Google Scholar search engines.

RESULTS

Neurodevelopmental delay and hypotonia were the commonest clinical signs of PDC deficiency. Structural brain abnormalities frequently included ventriculomegaly, dysgenesis of the corpus callosum and neuroimaging findings typical of Leigh syndrome. Neither gender nor any clinical or neuroimaging feature differentiated the various biochemical etiologies of the disease. Patients who died were younger, presented clinically earlier and had higher blood lactate levels and lower residual enzyme activities than subjects who were still alive at the time of reporting. Survival bore no relationship to the underlying biochemical or genetic abnormality or to gender.

CONCLUSIONS

Although the clinical spectrum of PDC deficiency is broad, the dominant clinical phenotype includes presentation during the first year of life; neurological and neuromuscular degeneration; structural lesions revealed by neuroimaging; lactic acidosis and a blood lactate:pyruvate ratio ≤20.

Pyruvate dehydrogenase deficiency and epilepsy

The pyruvate dehydrogenase complex (PDHc) is a mitochondrial matrix multienzyme complex that provides the link between glycolysis and the tricarboxylic acid (TCA) cycle by catalyzing the conversion of pyruvate into acetyl-CoA. PDHc deficiency is one of the commoner metabolic disorders of lactic acidosis presenting with neurological phenotypes that vary with age and gender. In this mini-review, we postulate mechanisms of epilepsy in the setting of PDHc deficiency using two illustrative cases (one with pyruvate dehydrogenase complex E1-alpha polypeptide (PDHA1) deficiency and the second one with pyruvate dehydrogenase complex E1-beta subunit (PDHB) deficiency (a rare subtype of PDHc deficiency)) and a selected review of published case series. PDHc plays a critical role in the pathway of carbohydrate metabolism and energy production. In severe deficiency states the resulting energy deficit impacts on brain development in utero resulting in structural brain anomalies and epilepsy. Milder deficiency states present with variable manifestations that include cognitive delay, ataxia, and seizures. Epileptogenesis in PDHc deficiency is linked to energy failure, development of structural brain anomalies and abnormal neurotransmitter metabolism. The use of the ketogenic diet bypasses the metabolic block, by providing a direct source of acetyl-CoA, leading to amelioration of some symptoms. Genetic counseling is essential as PDHA1 deficiency (commonest defect) is X-linked although females can be affected due to unfavorable lyonization, while PDHB and PDH phosphatase (PDP) deficiencies (much rarer defects) are of autosomal recessive inheritance. Research is in progress for looking into animal models to better understand pathogenesis and management of this challenging disorder.

Deletion at chromosomal band Xp22.12-Xp22.13 involving PDHA1 in a patient with congenital lactic acidosis

We present a patient with congenital lactic acidosis, agenesis of the corpus callosum, and profound developmental delay. Assays of pyruvate dehydrogenase complex function were normal in lymphocytes, but decreased in fibroblasts. Sequencing of the PDHA1 gene did not reveal deleterious mutations, and BAC based microarray analysis did not reveal any chromosomal abnormality. However, gene dosage analysis with oligonucleotide-based chromosomal microarray revealed a deletion of Xp22.12-Xp22.13 involving complete deletion of PDHA1. This is the first report of a whole gene deletion of PDHA1 detected by oligonucleotide-based microarray.

Solution structure and characterisation of the human pyruvate dehydrogenase complex core assembly

Mammalian pyruvate dehydrogenase complex (PDC) is a key multi-enzyme assembly that is responsible for glucose homeostasis maintenance and conversion of pyruvate into acetyl-CoA. It comprises a central pentagonal dodecahedral core consisting of two subunit types (E2 and E3BP) to which peripheral enzymes (E1 and E3) bind tightly but non-covalently. Currently, there are two conflicting models of PDC (E2+E3BP) core organisation: the 'addition' model (60+12) and the 'substitution' model (48+12). Here we present the first ever low-resolution structures of human recombinant full-length PDC core (rE2/E3BP), truncated PDC core (tE2/E3BP) and native bovine heart PDC core (bE2/E3BP) obtained by small-angle X-ray scattering and small-angle neutron scattering. These structures, corroborated by negative-stain and cryo electron microscopy data, clearly reveal open pentagonal core faces, favouring the 'substitution' model of core organisation. The native and recombinant core structures are all similar to the truncated bacterial E2 core crystal structure obtained previously. Cryo-electron microscopy reconstructions of rE2/E3BP and rE2/E3BP:E3 directly confirm that the core has open pentagonal faces, agree with scattering-derived models and show density extending outwards from their surfaces, which is much more structurally ordered in the presence of E3. Additionally, analytical ultracentrifugation characterisation of rE2/E3BP, rE2 (full-length recombinant E2-only) and tE2/E3BP supports the substitution model. Superimposition of the small-angle neutron scattering tE2/E3BP and truncated bacterial E2 crystal structures demonstrates conservation of the overall pentagonal dodecahedral morphology, despite evolutionary diversity. In addition, unfolding studies using circular dichroism and tryptophan fluorescence spectroscopy show that the rE2/E3BP is less stable than its rE2 counterpart, indicative of a role for E3BP in core destabilisation. The architectural complexity and lower stability of the E2/E3BP core may be of benefit to mammals, where sophisticated fine-tuning is required for cores with optimal catalytic and regulatory efficiencies.

Pyruvate dehydrogenase complex deficiency: four neurological phenotypes with differing pathogenesis

AIM

To describe the phenotype and genotype of pyruvate dehydrogenase complex (PDHc) deficiency.

METHOD

Twenty-two participants with enzymologically and genetically confirmed PDHc deficiency were analysed for clinical and imaging features over a 15-year period.

RESULTS

Four groups were identified: (1) those with neonatal encephalopathy with lactic acidosis (one male, four females; diagnosis at birth); (2) those with non-progressive infantile encephalopathy (three males, three females; age at diagnosis 2-9mo); (3) those with Leigh syndrome (eight males; age at diagnosis 1-13mo); and (4) those with relapsing ataxia (three males; 18-30mo). Seventeen mutations involved PDHA1 (a hotspot was identified in exons 6, 7, and 8 in seven males with Leigh syndrome or recurrent ataxia). Mutations in the PDHX gene (five cases) were correlated with non-progressive encephalopathy and long-term survival in four cases.

INTERPRETATION

Two types of neurological involvement were identified. Abnormal prenatal brain development resulted in severe non-progressive encephalopathy with callosal agenesis, gyration anomalies, microcephaly with intrauterine growth retardation, or dysmorphia in both males and females (12 cases). Acute energy failure in infant life produced basal ganglia lesions with paroxysmal dystonia, neuropathic ataxia due to axonal transport dysfunction, or epilepsy only in males (11 cases). The ketogenic diet improved only paroxysmal dysfunction, providing an additional argument in favour of paroxysmal energy failure.

A cognitively normal PDH-deficient 18-year-old man carrying the R263G mutation in the PDHA1 gene

Pyruvate dehydrogenase (PDH) is a crucial multienzyme system linking glycolysis to the tricarboxylic acid cycle by catalysing the decarboxylation of pyruvate to acetyl-CoA. Deficiency in pyruvate dehydrogenase is most commonly secondary to mutations in the X-linked PDHA1 gene encoding the E1 alpha subunit. There is a wide range of clinical presentations from severe neonatal lactic acidosis to chronic encephalopathy (Leigh syndrome). In recent years, a small subset of patients was recognized with less severe involvement, presenting initially only with intermittent symptoms, mainly of ataxia. Most of these patients remain stable for a number of years before developing progressive neurological deterioration around puberty at the latest. There does not appear to be a reliable correlation between genotype, phenotype, or enzyme activity. This makes counselling in a clinical setting challenging. We report a case with a previously known common mutation in PDHA1 (R263G) with an excellent outcome at 18 years of age. Previous patients with this mutation have presented with mental retardation and/or Leigh syndrome, while our patient's clinical outcome is exceptional. He is cognitively normal and has normal brain MRI. His management includes a stringent carbohydrate-free diet, as well as supplementation with thiamine, carnitine and vitamin E. This case further broadens the clinical spectrum, including now an example of a cognitively normal adult with PDH deficiency.

Brain MR imaging and proton MR spectroscopy in female mice with pyruvate dehydrogenase complex deficiency

Pyruvate dehydrogenase complex (PDC) deficiency is an inborn metabolic disorder that causes neurological abnormalities. In this report, a murine model of PDC deficiency was analyzed using histology, magnetic resonance (MR) imaging and MR spectroscopy (MRS) and the results compared to PDC-deficient female patients. Histological analysis of brains from PDC-deficient mice revealed defects in neuronal cytoarchitecture in grey matter and reduced size of white matter structures. MR results were comparable to previously published clinical MR findings obtained from PDC-deficient female patients. Specifically, a 15.4% increase in relative lactate concentration, 64.4% loss of N-acetylaspartate concentration and a near complete loss of discernable glutamine plus glutamate concentration were observed in a PDC deficient mouse compared to wild-type control. Lower apparent diffusion coefficients (ADCs) were observed within the brain consistent with atrophy. These results demonstrate the usefulness of this murine model to systematically evaluate the beneficial effects of dietary and pharmacological interventions.

Intermittent peripheral weakness as the presenting feature of pyruvate dehydrogenase deficiency

Two unrelated children presenting with episodic isolated peripheral weakness were found to have pyruvate dehydrogenase (PDH) deficiency (OMIM 312170) due to previously undescribed mutations (Pro250Thr, Arg88Cys) in the gene for the E1alpha subunit (PDHA1). Taken in context with the literature, these patients suggest that acute weakness initially resembling Guillain-Barré syndrome is a potentially reversible and probably underdiagnosed manifestation of PDH deficiency and that peripheral nerve function should be evaluated in PDH-deficient patients.

Leigh's disease due to a new mutation in the PDHX gene

OBJECTIVE

To describe the clinical course, neuroradiological presentation, biochemical and molecular studies of a new patient with pyruvate dehydrogenase complex (PDHc) deficiency. To compare this case with the data on other published cases.

METHODS

Brain magnetic resonance imaging (MRI), basal metabolic investigations with lactate measurements in body fluids, PDHc activity assay on cultured skin fibroblasts, immunoblot analysis and molecular studies (polymerase chain reaction [PCR] and sequencing procedures).

RESULTS

Our patient accused an unspecific encephalopathy for years and presented at 13 years of age an acute deterioration with basal ganglia necrosis and subcortical white matter involvement. PDHc deficiency was secondary to a large deletion (3913 bp) in the PDHX gene, which encodes E3 binding protein (E3BP) subunit.

INTERPRETATION

These data provide an additional case of E3BP deficiency with a unique and previously unreported deletion in the PDHX gene.

Therapeutic potential of dichloroacetate for pyruvate dehydrogenase complex deficiency

We reviewed the use of oral dichloroacetate (DCA) in the treatment of children with congenital lactic acidosis caused by mutations in the pyruvate dehydrogenase complex (PDC). The case histories of 46 subjects were analyzed with regard to diagnosis, clinical presentation and response to DCA. DCA decreased blood and cerebrospinal fluid lactate concentrations, and was generally well tolerated. DCA may be particularly effective in children with PDC deficiency by stimulating residual enzyme activity and, consequently, cellular energy metabolism. A controlled trial is needed to determine the definitive role of DCA in the management of this devastating disease.

Pyruvate dehydrogenase phosphatase deficiency: identification of the first mutation in two brothers and restoration of activity by protein complementation

CONTEXT

Pyruvate dehydrogenase phosphatase (PDP) deficiency has been previously reported as an enzymopathy, but the genetic basis for such a defect has never been established.

OBJECTIVE

The aim of this study was to identify the cause of the defect in two patients who presented with PDP deficiency.

PATIENTS

We studied two brothers of consanguineous parents who presented with neonatal hypotonia, elevated lactate, and less than 25% native pyruvate dehydrogenase complex (PDHc) activity in skin fibroblasts compared with controls. The activity of the complex could be restored to normal values by preincubation of the cells with dichloroacetate or by treating cell extracts with calcium.

RESULTS

These two individuals were found to be homozygous for a 3-bp deletion in the coding sequence of the PDP isoform 1 (PDP1), which removes the amino acid residue leucine from position 213 of the protein. A recombinant version of this protein was synthesized and found to have a very reduced (<5%) ability to activate purified PDHc. Reduced steady-state levels of PDP1 in the patient's fibroblasts coupled with the low catalytic activity of the mutant PDP1 resulted in native PDHc activity being reduced, but this could be corrected by the addition of recombinant PDP1 (wild type).

CONCLUSION

We have identified mutations in PDP1 in two brothers with PDP deficiency and have proven that the mutation is disease-causing. This is the first demonstration of human disease due to a mutation in PDP1.

Biochemical and structural brain alterations in female mice with cerebral pyruvate dehydrogenase deficiency

Pyruvate dehydrogenase complex (PDC) deficiency is an inborn metabolic disorder associated with a variety of neurologic abnormalities. This report describes the development and initial characterization of a novel murine model system in which PDC deficiency has been introduced specifically into the developing nervous system. The absence of liveborn male and a roughly 50% reduction in female offspring following induction of the X-linked mutation indicate that extensive deficiency of PDC in the nervous system leads to pre-natal lethality. Brain tissue from surviving females at post-natal days 15 and 35 was shown to have approximately 75% of wild-type PDC activity, suggesting that a threshold of enzyme activity exists for post-natal survival. Detailed histological analyses of brain tissue revealed structural defects such as disordered neuronal cytoarchitecture and neuropil fibers in grey matter, and reduced size of bundles and disorganization of fibers in white matter. Many of the histologic abnormalities resemble those found in human female patients who carry mutations in the X-linked ortholog. These findings demonstrate a requirement for PDC activity within the nervous system for survival in utero and suggest that impaired pyruvate metabolism in the developing brain can affect neuronal migration, axonal growth and cell-cell interactions.

Maternal Phenylketonuria Collaborative Study (MPKUCS)--the 'outliers'

Analysis of outcome data from 305 of the 414 offspring from the Maternal Phenylketonuria Collaborative Study (MPKUCS), plus 70 control offspring, revealed significant deficits in the IQ (intelligence quotient), as measured by the Wechsler Intelligence Scale for Children--Revised (WISC-R), when maternal metabolic control during pregnancy was delayed and/or inadequate. There were, however, 23 'outliers' (7.5% of the 305) in which the offspring's intellectual IQ was worse (n =10) or better (n =13) than expected. The aim of this study was to determine whether collection parameters were incomplete or whether these subjects were true biological variants influenced by other undetected factors or, perhaps, by modifier genes. Among the 10 offspring whose intellectual functioning was worse than expected, additional complications were uncovered that could explain the poor outcome. Four of the 13 offspring with higher than expected IQ had mothers with mild variants of PKU in which the insult to the fetus would not be expected to be as profound. For the other nine offspring whose intellectual performance was better than expected, there was no explanation, based on the parameters studied. We hypothesize that modifier genes will, at times, protect the fetus despite high maternal concentrations of phenylalanine. Not all offspring from the same (untreated) PKU mother may be similarly affected. Finding the source of these modifiers might effect the treatment of MPKU.

Pyruvate dehydrogenase E1alpha subunit deficiency in a female patient: evidence of antenatal origin of brain damage and possible etiology of infantile spasms

Enlargement of the lateral ventricles and atrophy of the brain were documented ultrasonographically in utero at as early as 28th week of gestation in a female patient with lactic acidosis due to deficiency of the pyruvate dehydrogenase E1alpha subunit, demonstrating that the changes characteristic of this disease can occur antenatally. The mechanism of infantile spasms in this disease may be linked to mosaicism of the brain cells involving the normal enzyme and the mutant enzyme.

Clinical spectrum and diagnosis of mitochondrial disorders

Respiratory chain deficiencies have long been regarded as neuromuscular diseases mostly originating from mutations in the mitochondrial DNA. Actually, oxidative phosphorylation, i.e., adenosine triphosphate (ATP) synthesis-coupled electron transfer from substrate to oxygen through the respiratory chain, does not only occur in the neuromuscular system. For this reason, 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, owing to the dual genetic origin of respiratory chain enzymes (nuclear DNA and mitochondrial DNA). In recent years, it has become increasingly clear that genetic defects of oxidative phosphorylation account for a large variety of clinical symptoms in both childhood and adulthood. Diagnosis of a respiratory chain deficiency is difficult initially when only one symptom is present, and easier when additional, seemingly unrelated, symptoms are observed. The clinical heterogeneity is echoed by the genetic heterogeneity illustrated by the increasing number of nuclear genes that have been shown to be involved in these diseases. In the absence of clear-cut genotype-phenotype correlations and in front of the large number of possibly involved genes, biochemical analyses are still the cornerstone of the diagnosis of this condition.

Laboratory approach to mitochondrial diseases

Dysfunction in mitochondrial processes has been related to several pathologies. In these disorders, the cell suffers oxidative imbalance that is mostly due to defects in pyruvate metabolism, mitochondrial fatty acids oxidation, the citric acid cycle or electron transport by the mitochondrial respiratory chain. These metabolic alterations produce mitochondrial diseases that have been related to inherited syndromes, such as MERRF or MELAS. The main affected organs are brain, skeletal muscle, kidney, heart and liver, because of the high energetic demand and the oxidative metabolism. Moreover, the relationship between mitochondrial dysfunction and neurodegenerative processes, such as Parkinson disease or Alzheimer disease, as well as ageing, has been shown. Because mitochondrias are the target of several xenobiotics, such as aspirin, AZT or alcohol consumption, mitochondrial impairment has also been proposed as a mechanism of toxicity. Most laboratory tests that are available in the diagnosis of mitochondrial illness are assayed in tissue biopsies and are usually difficult to interpret. Recently, it has been shown that non-invasive techniques, such as nuclear magnetic resonance or the 2-keto[1-(13)C]isocaproic acid breath test, may be useful to assess mitochondrial function. This article attempts to show the laboratory approach to mitochondrial diseases, reviewing new techniques that could be of great value in the research of mitochondrial function, such as the 2-keto[1-(13)C]isocaproic breath test.

Leigh disease: clinical, neuroradiologic, and biochemical study of three new cases with cytochrome c oxidase deficiency

Three cases of Leigh disease are described. In all three, symptoms began in the first months of life, with muscle hypotonia, lactic acidosis, and psychomotor delay. The diagnosis was made on the basis of the clinical characteristics, biochemical abnormalities, and typical brain magnetic resonance imaging with symmetric lesions suggesting bilateral necrosis at the level of the basal ganglia and of the midbrain. Cytochrome c oxidase (complex IV of the mitochondrial respiratory chain) deficiency was demonstrated in muscle tissue in all patients and confirmed in skin fibroblasts in patient 3. A genetic heterogeneity was present in these patients since only one had a SURF-1 gene mutation. The clinical, biochemical, and neuroradiologic aspects are discussed. Finally, the finding of facial dysmorphisms in the cytochrome c oxidase deficiency observed in one of the described cases is of extreme interest; to our knowledge, this association has never been reported in the literature.

Unique astrocytic inclusion in a 2 month-old baby showing Leigh-like brain lesions with lactic acidosis

An unique cytoplasmic inclusion was found in astrocytes of a 2-month-old female baby who showed Leigh-like brain lesions with lactic acidosis, hypoglycemia and hepatomegaly. Although a defective enzyme was not determined, a metabolic disorder was suggested from clinicopathological observations. Symmetrically distributed lesions consisting of marked gliosis and proliferation of capillaries were observed in the basal ganglia, thalami and tegmentum. The astrocytic cytoplasmic inclusion was exclusively found in the cerebral and cerebellar white matter, where myelination was immature. The inclusion was round and eosinophilic, and positive for glial fibrillary acidic protein, vimentin, alphaB-crystallin, S-100 protein and microtubule associated protein 1B, immunohistochemically. An electron microscopic examination revealed an accumulation of intermediate filaments, ribosome and rough endoplasmic reticulum in the inclusion. The characteristic of this inclusion is different from that of other reported inclusions. The inclusion showed positive immunoreaction against CuZn superoxide dismutase, catalase, advanced glycation end-product and 4-hydroxy-2-nonenal antibodies, which suggest that oxidative stress is involved in the genesis of the inclusion.