PDHC Deficiency Research Articles

Neurophysiological profile of peripheral neuropathy associated with childhood mitochondrial disease

IntroductionPeripheral nerve involvement is common in mitochondrial disease but often unrecognised due to the prominent central nervous system features. Identification of the underlying neuropathy may assist syndrome classification, targeted genetic testing and rehabilitative interventions. MethodsClinical data and the results of nerve conduction studies were obtained retrospectively from the records of four tertiary children's hospital metabolic disease, neuromuscular or neurophysiology services. Nerve conductions studies were also performed prospectively on children attending a tertiary metabolic disease service. Results were classified and analysed according to the underlying genetic cause. ResultsNerve conduction studies from 27 children with mitochondrial disease were included in the study (mitochondrial DNA (mtDNA) – 7, POLG – 7, SURF1 – 10, PDHc deficiency – 3). Four children with mtDNA mutations had a normal study while three had mild abnormalities in the form of an axonal sensorimotor neuropathy when not acutely unwell. One child with MELAS had a severe acute axonal motor neuropathy during an acute stroke-like episode that resolved over 12months. Five children with POLG mutations and disease onset beyond infancy had a sensory ataxic neuropathy with an onset in the second decade of life, while the two infants with POLG mutations had a demyelinating neuropathy. Seven of the 10 children with SURF1 mutations had a demyelinating neuropathy. All three children with PDHc deficiency had an axonal sensorimotor neuropathy. Unlike CMT, the neuropathy associated with mitochondrial disease was not length-dependent. ConclusionsThis is the largest study to date of peripheral neuropathy in genetically- classified childhood mitochondrial disease. Characterising the underlying neuropathy may assist with the diagnosis of the mitochondrial syndrome and should be an integral part of the assessment of children with suspected mitochondrial disease.

G471 Somatic mosaicism in X-linked PDHA1 gene – a cause of developmental delay and epilepsy

BackgroundPyruvate dehydrogenase complex (PDHc) deficiency is an inborn error of metabolism that occurs most commonly due to mutations in the X-linked E1α subunit gene (PDHA1). PDHc plays a critical role...

A 1.1 Million Base Pair X-Chromosomal Deletion Covering the PDHA1 and CDKL5 Genes in a Female Patient with West Syndrome and Pyruvate Oxidation Deficiency

Mutations in the X-linked E1α subunit of the pyruvate dehydrogenase complex (PHDC) are the most frequent causes of PDHC deficiency. The clinical picture is heterogeneous depending on residual enzyme activity and X-inactivation. We report on a girl who presented at an age of 3 weeks with muscular hypotonia, vomiting, hyperlactatemia, microcephaly, enlarged ventricles, partial agenesis of the corpus callosum, and seizures. PDHA1 sequencing was normal in DNA from blood. In muscle, normal PDHC activity was measured while substrate oxidation rates revealed moderately diminished pyruvate oxidation. Quantitative PCR analysis revealed hemizygosity of the whole PDHA1 gene. Homozygosity mapping and determination of the breakpoint showed a 1.1 million base pair deletion on the X-chromosome including the CDKL5 and PDHA1 genes. The difficulty in the diagnosis of PDHC deficiency is evident: (1) enzyme activity can be normal depending on the X-inactivation; (2) large deletions can be missed by routine genetic analysis; and (3) only quantification of the PDHA1 gene content revealed the mutation in our patient. We recommend to revisit patients who are clinically suspicious for a mitochondrial disorder especially for hidden PDHA1 mutations, such as large deletions.

Dihydrolipoamide dehydrogenase (DLD) deficiency in a Spanish patient with myopathic presentation due to a new mutation in the interface domain

We present a 32-year-old patient who, from age 7 months, developed photophobia, left-eye ptosis and progressive muscular weakness. At age 7 years, she showed normal psychomotor development, bilateral ptosis and exercise-induced weakness with severe acidosis. Basal blood and urine lactate were normal, increasing dramatically after effort. PDHc deficiency was demonstrated in muscle and fibroblasts without detectable PDHA1 mutations. Ketogenic diet was ineffective, however thiamine gave good response although bilateral ptosis and weakness with acidosis on exercise persisted. Recently, DLD gene analysis revealed a homozygous missense mutation, c.1440 A>G (p.I480M), in the interface domain. Both parents are heterozygous and DLD activity in the patient's fibroblasts is undetectable. The five patients that have been reported with DLD-interface mutations suffered fatal deteriorations. Our patient's disease is milder, only myopathic, more similar to that due to mutation p.G229C in the NAD(+)-binding domain. Two of the five patients presented mutations (p.D479V and p.R482G) very close to the present case (p.I480M). Despite differing degrees of clinical severity, all three had minimal clues to DLD deficiency, with occasional minor increases in α-ketoglutarate and branched-chain amino acids. In the two other patients, hypertrophic cardiomyopathy was a significant feature that has been attributed to moonlighting proteolytic activity of monomeric DLD, which can degrade other mitochondrial proteins, such as frataxin. Our patient does not have cardiomyopathy, suggesting that p.I480M may not affect the DLD ability to dimerize to the same extent as p.D479V and p.R482G. Our patient, with a novel mutation in the DLD interface and mild clinical symptoms, further broadens the spectrum of this enzyme defect.

Mutational study in the PDHA1 gene of 40 patients suspected of pyruvate dehydrogenase complex deficiency

We screened for PDHA1 mutations in 40 patients with biochemically demonstrated PDHc deficiency or strong clinical suspicion, and found changes with probable pathological significance in 20. Five patients presented new mutations: p.A169V, c.932_938del, c.1143_1144 ins24, c.1146_1159dup and c.510-30G> A, this latter is a new undescribed cause of exon 6 skipping. Another four mutations have been found, and previously reported, in our patients: p.H113D, p.P172L, p.Y243del and p.Y369Q. Eleven patients presented seven known mutations: p.R127Q, p.I166I, p.A198T, p.R263G, p.R302C, p.R378C and c.1142_1145dup. The latter three were found in more than one unrelated patient: p.R302C was detected in a heterozygous girl and a mosaic male, p.R378C in two males and finally, c.1142_1145dup in three females; only one in 20 mothers was found to be a carrier (p.R263G). Apart from those 20 patients, the only alteration detected in one girl with clear PDHc and PDH-E1 deficiency was the silent change c.396A> C (p.R132R), and other eight PDHc deficient patients carry combinations of known infrequent polymorphisms that are overrepresented among our 20 unsolved patients. The importance of these changes on PDH activity is unclear. Investigations in the other PDHc genes are in course in order to elucidate the genetic defect in the unresolved patients.

146 Difficulty in the diagnosis of X-linked PDHC deficiency due to a large deletion affecting the PDHA1 gene

146 Difficulty in the diagnosis of X-linked PDHC deficiency due to a large deletion affecting the PDHA1 gene

Females with PDHA1 gene mutations: A diagnostic challenge

Biochemical analysis was performed in muscle tissue and in fibroblasts of four unrelated females consecutively diagnosed with a ‘de novo’ point mutation in the PDHA1 gene. Pyruvate dehydrogenase E1 subunit deficiency was confirmed in the muscle sample of all patients, however, in three out of four cases the activity of the pyruvate dehydrogenase complex in fibroblasts showed a normal activity. A skewed inactivation was confirmed of the maternal X chromosome in fibroblasts in all children. Due to the possibility of a skewed X inactivation pattern enzyme measurements in fibroblasts are not always reliable for the diagnosis of a PDHc defect in females. Based on the overlapping features of PDHc deficiency with those of the disorders of the oxidative phosphorylation we suggest performing a fresh muscle biopsy for detailed biochemical analysis in females with a suspected pyruvate dehydrogenase deficiency, followed by molecular genetic analysis of the PDHA1 gene.

Organic acidemias in Korea - Eight years experience of organic acid analysis -

Purpose:We have done this retrospective study to know the relative incidence and clinical manifestations of organic acidopathies in Korea during 8 years(from Jul. 1997 to May 2005). This results of organic acid analysis of 1,787 patients were compared with the results of organic acid analysis that were published three years ago. Methods:The results of quantitative organic acid analysis of samples of 1788 patients, referred from Jul. 1997 to May 2005, were analyzed retrospectively according to four age group(-2 mon, 3 mon-2 years, 3-12 years) and major clinical manifestations. Quantification of 83 organic acids was done with gas chromatography and mass spectometry. Results:We diagnosed 470 patients with 27 diseases of organic acid metabolism during this study period. Diseases found more than 10 cases are cytosolic 3-ketothiolase deficiency, mitochondrial respiratory chain disorders, PDHC deficiency, mitochondrial 3-ketothiolase deficiency, glutaric aciduria type II, biotinidase deficiency, methylmalonic aciduria and propionic aciduria. Other diseases were diagnosed in less than 10 cases. Conclusion:Though the incidence of individual organic acidemia is low, the overall incidence of organic acidemia as a whole seems to be relatively high in Korea. Compared with the results of organic acid analysis that were reported three years ago, we couldn't find a new disease and the difference of the relative incidences of high incident diseases. We were apprehensive of the errors that was owing to the short study period(3 years), but the relative incidences of our study(8 years) were similar to the results of organic acid analysis that were reported three years ago.

Mitochondrial tRNA gene mutations in patients having mitochondrial disease with lactic acidosis

Lactic acidosis has been associated with a variety of clinical conditions and can be due to mutation in nuclear or mitochondrial genes. We performed mutations screening of all mitochondrial tRNA genes in 44 patients who referred as hyperlactic acidosis. Patients showed heterogeneous phenotypes including Leigh disease in four, MELAS in six, unclassified mitochondrial myopathy in 10, cardiomyopathy in five, MERRF in one, pure lactic acidosis in six, and others in 12 including facio-scaplo-femoral muscular dystrophy (FSFD), familial cerebellar ataxia, recurrent Reye syndrome, cerebral palsy with mental retardation. We measured enzymatic activities of pyruvate dehydrogenase complex, and respiratory chain enzymes. All mitochondrial tRNA genes and known mutation of ATPase 6 were studied by single strand conformation polymorphism (SSCP), automated DNA sequence and PCR-RFLP methods. We have found one patient with PDHC deficiency and six patients with Complex I+IV deficiency, though the most of the patients showed subnormal to deficient state of respiratory chain enzyme activities. We have identified one of the nucleotide changes in 29 patients. Single nucleotide changes in mitochondrial tRNA genes are found in 27 patients and one in ATPase 6 gene in two patients. One of four pathogenic point mutations (A3243G, C3303T, A8348G, and T8993G) was identified in 12 patients who showed the phenotype of Leigh syndrome, MELAS, cardimyopathy and cerebral palsy with epilepsy. Seventeen patients have one of the normal polymorphisms in the mitochondrial tRNA gene reported before. SSCP and PCR-RFLP could detect the heteroplasmic condition when the percentage of mutant up to 5, however, it cannot be observed by direct sequencing method. It is important to screen the mtDNA mutation not only by direct sequence but also by PCR-RFLP and the other sensitive methods to detect the heroplasmy when lactic acidosis has been documented in the patients who are not fulfilled the criteria of mitochondrial disorders.

A family with pyruvate dehydrogenase complex deficiency due to a novel C>T substitution at nucleotide position 407 in exon 4 of the X-linked Ε1α gene

The pyruvate dehydrogenase complex (PDHc; McKusick 312170), localised in the mitochondrial matrix, is a multienzyme complex which converts pyruvate to acetyl-CoA. A deficiency of PDHc leads to inadequate removal of pyruvate and lactate resulting in lactic acidaemia and insufficient energy production. The major cause of PDHc deficiency is a defect in the E1alpha component. The gene of this component is localised to Xp22.1. We describe two brothers with a relatively mild clinical phenotype of PDHc deficiency. Onset of disease was associated with muscle weakness and swallowing difficulties in both. At follow-up, the older brother developed encephalopathic features consistent with Leigh syndrome. Lactate to pyruvate ratios were low, consistent with a PDHc deficiency which was confirmed by measurements of PDHc activity in thrombocytes. A 407C>T change in exon 4 of the E1alpha gene was found in both brothers and their mother. This substitution predicts a replacement of a conserved alanine at position 136 by valine. Due to the X-linked inheritance pattern combined with the overall results of clinical investigations, molecular genetic findings and a corresponding functional deficiency of the gene product we believe that this substitution in the pyruvate dehydrogenase E1alpha gene is a mutation leading to pyruvate dehydrogenase complex deficiency in this family.

Differential effect of DCA treatment on the pyruvate dehydrogenase complex in patients with severe PDHC deficiency.

Dichloroacetate (DCA) is a structural analog of pyruvate that has been recommended for the treatment of primary lactic acidemia, particularly in patients with pyruvate dehydrogenase (PDHC) deficiency. Recent reports have demonstrated that the response to DCA may depend on the type of molecular abnormality. In this study, we investigated the response to DCA in various PDHC-deficient cell lines and tried to determine the mechanism involved. The effect of chronic 3-d DCA treatment on PDHC activity was assessed in two PDHC-deficient cell lines, each with a different point mutation in the E1alpha subunit gene (R378C and R88C), and one cell line in which an 8-bp tandem repeat was deleted (W383 del). Only two (R378C and R88C) of the three PDHC-deficient cell lines with very low levels of PDHC activity and unstable polypeptides were sensitive to chronic DCA treatment. In these cell lines, DCA treatment resulted in an increase in PDHC activity by 125 and 70%, respectively, with concomitant increases of 121 and 130% in steady-state levels of immunoreactive E1alpha. DCA treatment reduced the turnover of the E1alpha subunit in R378C and R88C mutant cells with no significant effect on the E1beta subunit. Chronic DCA treatment significantly improved the metabolic function of PDHC in digitonin-permeabilized R378C and R88C fibroblasts. The occurrence of DCA-sensitive mutations suggests that DCA treatment is potentially useful as an adjuvant to ketogenic and vitamin treatment in PDHC-deficient patients.

COMBINED DEFICIENCY OF PYRUVATE DEHYDROGENASE AND MITOCHONDRIAL RESPIRATOR CHAIN COMPLEX I: CASE REPORT

We described a male child of two years and three months affected by assial hypotonia, psicomotor retardation, muscular distal hypotrophy with hyporeflexia, dystonic movements and deafness. He was born from non‐consanguineous parents by spontaneous caesarian twin delivery at 38 weeks. His sister is healthy. He came to our observation at 16 months of age. Screenings for metabolic diseases and CSF neurotransmitters and lactate were normal, whereas the serum lactate was mildly increased. Brain MRI showed delayed myelination, with the normal lactate at the spectroscopic study. EEG showed interemispheric asymmetry with epileptic discharges. EMG showed a neurogenic pattern. Molecular DNA analysis for Spinal Muscular Atrophy was negative. Muscle biopsy showed neurogenic injury and an absence of ragged red fibers; enzymatic assay showed a severe deficiency of Complex I (2.8 nmol/min/mg protein, n.v. 17–33) and a mild deficiency of Pyruvate Dehydrogenase (PDHC=0.47 nmol/min/mg protein, n.v.0.8‐2).The clinical features of patients with a dysfunction in mitochondrial metabolic pathways are variable. A PDHC deficiency leads to a graduated spectrum of neurological involvement starting from severe forms with death in the neonatal period, Leigh disease and carbohydrate‐induced episodic ataxia. The most common features associated with a PDHC defect are delayed development and hypotonia. Patients with Complex I deficiency show a variable phenotype from fatal infantile encephalomyopathy to adult‐onset myopathy; neurodegenerative disorders are also described: Parkinson's disease, dystonia and Leber's optic neuropathy. A combined PHDC and Complex I deficiency is rarely reported. We can make the hypothesis that a defect of a single enzyme (Complex I) can play a role on the other enzyme deficiency. The presence of a primitive PHDC and Complex I deficiency is unlikely be hypothesized since the parents are not consanguineous and a double genetic defect is improbable.

Mitochondrial myopathies.

The mitochondrial myopathies or encephalomyopathies with known biochemical defects can be divided into 5 groups: (1) defects of mitochondrial transport, such as CPT deficiency or carnitine deficiencies; (2) defects of substrate utilization, such as PDHC deficiency or defects of beta-oxidation; (3) defects of the Krebs cycle, such as fumarase deficiency; (4) defects of oxidation-phosphorylation coupling, such as Luft disease, and (5) defects of the respiratory chain. These disorders are reviewed, with particular emphasis on the defects of the respiratory chain. Defects of complex I, III and IV show remarkable clinical and biochemical heterogeneity. All 3 complexes contain some subunits encoded by mtDNA and others encoded by nuclear DNA. At least some of the cytoplasmically made subunits appear to be tissue specific and may be developmentally regulated, thus explaining the genetic heterogeneity of these disorders.

An immunochemical study of the pyruvate dehydrogenase deficit in Alzheimer's disease brain.

The activity of the pyruvate dehydrogenase complex (PDHC; EC 1.2.4.1, EC 2.3.1.12, and EC 1.6.4.3) was reduced to about 30% of control values in histologically unaffected occipital cortex of the brains of patients with Alzheimer's disease, as well as in histologically affected frontal cortex. In contrast, activity of another mitochondrial enzyme, glutamate dehydrogenase, was normal. Neither age nor time until postmortem study correlated significantly with PDHC activity in either Alzheimer or control samples, and PDHC was not inactivated significantly on incubation with homogenates of either Alzheimer or control brain. Antibodies against the highly purified bovine PDHC inhibited Alzheimer and control PDHC equally per unit of enzyme activity. Immunoblots also indicated that the PDHC antigens were not different in normal and Alzheimer brains. This antibody, however, inhibited Alzheimer PDHC more effectively than it did control PDHC, based on milligrams of protein, suggesting a reduced amount of normal PDHC protein. Other data suggest that the PDHC deficiency is related to mitochondrial damage and to impaired calcium homeostasis in Alzheimer nerve cells, which may then mediate a variety of other cellular impairments.