A possible mechanism for selective cerebellar damage in partial pyruvate dehydrogenase deficiency

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.

Some Observations upon Biochemical Causes of Ataxia and a New Disease Entity Ubiquinone, CoQ10 Deficiency

Some hereditary ataxias are treatable and the insight required for this has come from an in depth knowledge of the phenotypes and clinical biochemistry of the conditions. This has required both fundamental and translational clinical research. Prof John Blass was fortunate to begin his career at what we can now recognise as a golden era for such studies and he worked upon two important conditions; Refsum's disease and Friedreich's ataxia. More recently the mitochondrial encephalomyopathies have been described and similar investigative work has been undertaken upon them. Ubiquinone, CoQ(10), deficiency is the most recently recognised encephalomyopathy and is itself treatable. Though rare, it is becoming increasingly recognised and patients are benefiting from the same scholarly approach to its investigation as was afforded Refsums' disease and Friedreich's ataxia.

Determination of specific activities and kinetic constants of biotinidase and lipoamidase in LEW rat and Lactobacillus casei (Shirota)

Enzyme kinetic parameters, such as K(m), V(max) (or V), k(cat)/K(m), and K(i) (by biotin or lipoic acid) for biotinidase and lipoamidase were determined in Lewis (LEW) rat and Lactobacillus casei (Shirota) using fluorimetric high-performance liquid chromatography (HPLC). It was found that the final protein concentration below 0.1mg/ml is sufficient to obtain linear hydrolytic reaction and to determine the Michaelis-Menten type kinetic parameters (K(m), V, K(i)). We applied this HPLC enzyme assay method onto the rat and some bacteria. The highest specific activities (Vs) for biotinidase were found in Lactobacillus casei (Shirota) and rat kidney. It was also found that the largest K(i) by product for biotinidase and lipoamidase were present in the Lactobacillus casei (Shirota). There has been found specie (between rat and mouse) differences and tissue (organ) differences, together with tissue region differences and sex differences in some tissues. Summary of the distributions of both enzymes in LEW rat was also presented. Therefore, this HPLC determination method for the enzyme kinetic parameters in tissues is expected to be an indispensable tool for the investigation of the various diseases in humans.

53-years-old with mental status changes

D-lactic acidosis, a complication of short bowel syndrome, presents with a variety of neurological symptoms and metabolic acidosis. Treatment is hydration, replacement of nutritional deficiency replacement, and selective antibiotics. Prevention entails complex carbohydrate diet and vitamin and mineral supplements.

Neuroradiological features of six kindreds with MELAS tRNA(Leu) A2343G point mutation: implications for pathogenesis

OBJECTIVE

To determine the neuroradiological abnormalities associated with subjects carrying the mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes (MELAS) tRNA(Leu)(UUR) A3243G point mutation

METHODS

Mitochondrial genetic analysis was performed on 24 subjects from six kindreds with the MELAS tRNA(Leu)(UUR) A3243G point mutation. Cerebral CT and MRI were performed on 24 patients and 15 patients respectively. Previous neuroradiological investigations including cerebral CT from four deceased members of the families were also reviewed. Histological examination of postmortem specimens of two patients within the kindreds was performed.

RESULTS

The commonest radiological finding was basal ganglia calcification. Other abnormalities included focal lesions and cerebellar and cerebral atrophy. Basal ganglia calcification was progressive, symmetric, and asymptomatic. Histologically, basal ganglia calcification in one patient was found to be in the pericapillary regions of the globus pallidus, with no neuronal involvement. Focal lesions most commonly involved the grey matter of the parietal and occipital lobes and cerebellum. Histopathological examination suggested that these were due to cellular rather than vascular dysfunction. Enlargement of the fourth ventricle was the first sign of cerebellar atrophy. Cerebral and cerebellar atrophy were only present with severe disease.

CONCLUSIONS

These radiological findings, when considered in the context of the clinical and pathological findings, seem to reflect two major disease processes: an intermittent abrupt loss of function associated with cell injury from which there is at least partial recovery and a slowly progressive degenerative process causing basal ganglia calcification, and cerebral and cerebellar atrophy. The clinical and radiological features resulting from these processes are distinctive and provide insight into the consequences of mitochondrial dysfunction on the brain.

Episodic ataxia and channelopathies

Clinical details are given of different types of episodic ataxia: type 1, with myokymia, and attacks which usually last a few minutes, and may occur several times a day, and treatment with acetazolamide can reduce the number of attacks; type 2, with interictal nystagmus, and attacks which last for several hours to a day or more, and treatment with acetazolamide is very effective; paroxysmal choreoathetosis with episodic ataxia, with attacks lasting for about 20 min and occurring at varying intervals; and familial hemiplegic migraine, with transient hemiplegia presenting during the aura of a migraine headache, the symptoms improving on treatment with acetazolamide. Their inheritance is of dominant type; and the gene for type 1 is mapped to chromosome 12p near to a cluster of potassium channel genes, and that for type 2 and for familial hemiplegic migraine to chromosome 19p near to calcium channel genes. The differential diagnosis from other conditions with a periodic symptomatology is discussed, especially from a number of metabolic disorders. Treatment is effective for many of these, and the treatment of the episodic ataxias with acetazolamide can sometimes have a dramatic effect. The possible role of the channelopathies in the causation of some periodic neurological disorders is considered; with the expectation that further research will improve the identification of specific diseases, and lead to more effective treatment.

Familial hemiplegic migraine, nystagmus, and cerebellar atrophy

Familial hemiplegic migraine (FHM) is an autosomal dominant disorder characterized by transient hemiplegia during the aura phase of a migraine attack. Nystagmus has been reported in individuals affected with this disorder, but the origin of the ocular motility findings is unknown. A three-generation family with FHM is described and clinical histories are outlined. Ocular motility evaluations were performed on 7 family members, 5 with a history of hemiplegic migraine and 2 without history of migraine. All affected family members had abnormal eye movements consistent with vestibulocerebellar dysfunction. Magnetic resonance imaging scans in affected family members revealed cerebellar vermian atrophy. DNA linkage analysis revealed a common marker in all the affected family members on chromosome 19. We suggest that the hemiplegic migraine attacks and the cerebellar degeneration are linked genetically and that the eye movements are not the ischemic sequelae of recurrent migraine. Strikingly similar ocular motility findings and cerebellar degeneration are reported in both FHM and a genetically related disorder, hereditary paroxysmal cerebellar ataxia (HPCA). The significance of these similarities is discussed along with a proposed pathophysiology for FHM.

Clinical diversity of pyruvate dehydrogenase deficiency

Clinical features, magnetic resonance, and biochemical studies are reported in 7 children with pyruvate dehydrogenase (PDH) deficiency. These findings confirm the diverse clinical presentation of this condition, although neurological abnormalities are consistent features. Imaging results are also varied. Six of the children were investigated with proton magnetic resonance spectroscopy and lactate was demonstrated in brain in all patients. Regional variation in the lactate signal was observed in those patients in whom 2 regions were examined. Advances in molecular genetics have provided some explanations for the clinical variation in pyruvate dehydrogenase deficiency.

Neuropathological findings of a patient with pyruvate dehydrogenase E1 alpha deficiency presenting as a cerebral lactic acidosis

Neuropathological findings are reported of a 6-month-old female child with a "cerebral" lactic acidosis. A mutation in the pyruvate dehydrogenase (PDH) E1 alpha gene was found. Gross examination of the brain revealed a severe thinning of the cerebral parenchym, a marked hydrocephalus sparing the aqueduct and fourth ventricle, agenesis of the corpus callosum and heterotopic noduli of gray matter in subependymal regions. Microscopical examination showed heterotopic inferior olives, absent pyramids and focal neuroglial overgrowth into meninges. In addition some heterotopia of Purkinje cells and dysplasia of the dentate nuclei were observed. There was a marked vascular proliferation with many thin-walled, congestive vessels in the cerebral and cerebellar white matter, and to a lesser extent in the striatum. To our knowledge these cerebellar and vascular abnormalities have not been reported before in patients with "cerebral" lactic acidosis. The combination of these neuropathological findings might be characteristic for PDH deficiency and more specifically for its E1 alpha subtype. Neuropathological examination could lead to the retrospective diagnosis of PDH E1 alpha deficiency in those cases where biochemical investigations were not or incompletely performed. This may have potential implications for genetic counseling.

Familial paroxysmal ataxia: report of a family

Three cases from one kindred who suffer from dominant paroxysmal ataxia are described. This is a rare benign non-progressive disorder of childhood onset, characterised by bouts of ataxia with abrupt onset lasting minutes or hours. Cases may be identified on the basis of a suggestive history, nystagmus persisting between episodes, and dominant inheritance. Treatment with acetazolamide is often dramatically effective. This family is thought to be the first described in the UK but many more probably exist, mislabelled as epilepsy or migraine.

Familial periodic cerebellar ataxia: a problem of cerebellar intracellular pH homeostasis

Six affected members of two families with familial periodic cerebellar ataxia were relieved of their symptoms with oral acetazolamide. Phosphorus 31 (31P) nuclear magnetic resonance spectroscopy showed abnormal intracellular pH levels in the cerebellum of all subjects when they were not treated. These levels returned to normal with treatment. Cerebral pH values were also measured in one family and were normal before and after treatment. An additional 3 patients with similar attacks, but without a family history, had normal untreated pH values in the cerebellum and cerebrum.

Organic acidurias: a review. Part 1

Organic acidemias are disorders of intermediary metabolism that lead to accumulation of organic acids in biologic fluids, disturb acid-base balance, and derange intracellular biochemical pathways. Their clinical presentation reflects the resultant systemic disease and progressive encephalopathy. While in some organic acidemias, disturbed acid-base metabolism is the predominant presenting feature, in others it is less prominent or even absent. The etiologies of the more than 50 different phenotypes include impaired metabolism of branched-chain amino acids, vitamins, glucose, lipids, glutathione, and gamma-aminobutyric acid and defects of oxidative phosphorylation. Most organic acidemias present with neurologic manifestations, which include acutely or subacutely progressive encephalopathy that involves different parts of the nervous system. The age of presentation and the associated systemic, hematologic, and immune findings provide additional guidelines for differential diagnosis. We summarize major organic acidemias, while emphasizing their usual and unusual neurologic presentations.

Reversible inhibition of acetylcholine synthesis and behavioural effects caused by 3-bromopyruvate

3-Bromopyruvate inhibits pyruvate decarboxylase in brain homogenates and causes a 90% drop in acetylcholine tissue content at a concentration of 2 mM. Stereotaxic injection of 3-bromopyruvate into the basal forebrain causes after 7 days a 40% drop of acetylcholine concentration and pyruvate decarboxylase activity in the cortex and hippocampus, and greater decreases at the site of injection. However, values return to normal 18 days after injection. Choline acetyltransferase is partially inhibited only at the site of injection after 7 days. Choline transport and choline concentration are not affected at either 7 or 18 days after injection. Impairments in spontaneous alternation and in retention of passive avoidance were seen only 7 days after the injection. The results suggest that stereotaxic injection of bromopyruvate can induce discrete reversible cholinergic lesions on a time scale useful for behavioural experiments and for comparison with neurodegeneration.

Deficiency of the alpha and beta subunits of pyruvate dehydrogenase in a patient with lactic acidosis and unexpected sudden death

An infant with moderate muscular hypotonia and congenital lactic acidosis died suddenly at the age of 3 months. Autopsy revealed no abnormalities responsible for this unexpected death. Measurement of mitochondrial enzymes involved in energy production indicated a severely decreased total pyruvate dehydrogenase complex (PDHC) activity in muscle tissue (0.23 nmoles x min-1 x mg protein-1, control range 2.8-8.7) and moderately decreased PDHC activity in fibroblasts (0.27 nmoles x min-1 x mg protein-1, control range 0.37-2.32). The activity of the first component E1 (pyruvate dehydrogenase) in muscle tissue was 10 times lower than that of controls (0.008 nmoles x min-1 x mg protein-1, control range 0.10-0.25). The activities of dihydrolipoyl dehydrogenase (E3) and various other mitochondrial enzymes were normal. Immunochemical analysis in skeletal muscle tissue and fibroblasts demonstrated a decrease in the amount of the alpha and beta subunits of E1. The features of this patient are compared with those of other patients reported in the literature with immunochemically confirmed combined E1 alpha and beta deficiency.

Lipoamidase (lipoyl-X hydrolase) from pig brain

Although the optimum substrate for lipoamidase (lipoyl-X hydrolase) has not yet been determined, it is known that lipoamidase activity, as determined by hydrolysis of the synthetic substrate lipoyl 4-aminobenzoate (LPAB), is widely distributed in pig brain tissues, i.e. in the cerebrum, cerebellum and medulla. Over 95% of the enzyme activity is present in the membrane subfractions, indicating that brain lipoamidase is an integral membrane protein enzyme. To elucidate the chemical nature and the optimum substrate of the abundant lipoamidase in the brain, we isolated it from the membrane subfractions. After an 8-step purification procedure, brain lipoamidase was purified 601-fold and identified as a 140 kDa glycoprotein by SDS/PAGE. A mechanistic study to determine Km and Vmax, values was carried out using various synthetic compounds. Lipoyl-lysine, which is generally believed to be a naturally occurring substrate of lipoamidase, was first compared with biotinyl-lysine, because these two vitamins have reactive sulphur atoms and are similar in molecular mass and structure. The Km for lipoyl-lysine was 333 microM, whereas biotinyl-lysine was not hydrolysed. Stringent specificity for the lipoyl moiety is demonstrated, as expected. Dipeptides of amino acid-lysine structures were studied, and dipeptides of aspartyl- and glutamyl-lysine hydrolysis occurred at high Km (3 mM) values. Thus lysine in the moiety is not very effective as an optimum substrate. The chemical bond structures of the amide bond (lipoyl-lysine) and peptide bond (aspartyl-lysine) were hydrolysed. Next, the ester bond compound was tested, and it was observed that lipolylmethyl ester was hydrolysed at high specificity. These findings indicate that this enzyme has broad specificities with respect to bond structure; it therefore is a unique hydrolase having stringent specificity for lipoic acid and relatively broad specificity for the chemical bond and the X moiety. Various inhibitors were tested; a few reagents, such as organic mercurials, di-isopropylfluorophosphate, 1,10-phenanthroline, sodium azide and angiotensin-converting enzyme inhibitor exhibited some inhibition (not more than 60%). Thus the active centre of this enzyme is a complex type. Although ATP is not hydrolysed and the lowest Km value is exhibited by the synthetic substrate reduced from LPAB (12 microM), some other compounds may still be expected to be hydrolysed by this unique and abundant brain lipoamidase.

Familial periodic ataxia

A teen-age girl presented with recurrent stereotyped episodes of vertigo and ataxia and manifested constant horizontal gaze-evoked nystagmus. Cranial computed tomographic scans and metabolic biochemical screens gave normal results. The diagnosis of familial periodic ataxia was made from the family history and examination of the family members. Familial periodic ataxia is a rare disorder of cerebellar function which is inherited dominantly and has a benign prognosis. The underlying pathophysiology remains uncertain but a therapeutic response frequently is achieved with acetazolamide.

Cytochrome c oxidase deficiency in Leigh syndrome

We studied 6 mitochondrial enzymes in crude extracts and isolated mitochondria from 5 children with pathologically proven subacute necrotizing encephalomyelopathy (Leigh syndrome). Samples were taken from brain (5 patients), skeletal muscle (4 patients), liver (4 patients), kidney (4 patients), heart (1 patient), and cultured fibroblasts (3 patients). An isolated defect of cytochrome c oxidase (COX) activity was found in brain (decrease of activity to 15 to 39% of the normal mean), muscle (9 to 20%), kidney (1 to 67%), and in the 1 available heart (4%) from a patient with cardiopathy. COX activity was also decreased in liver of 3 patients (2 to 13% of normal) and in cultured fibroblasts of 2 patients (18 and 27%), but it was normal in both liver and fibroblasts from 1 patient. Immunotitration using polyclonal antibodies against human heart COX showed essentially normal amounts of cross-reacting enzyme protein in various tissues from different patients. Electrophoresis of COX immunoprecipitated from brain mitochondrial extracts showed normal patterns of COX subunits in 2 patients. This study confirms the theory that COX deficiency is an important cause of Leigh syndrome.

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

Clinical findings are presented for 30 patients with lactic acidemia in whom activity of the pyruvate dehydrogenase complex in fibroblasts was significantly (P = less than 0.01) below that of control cell lines. Residual activity of the activated complex ranged from 1.6% to 68.5% of control activity. Seven patients died before 6 months of age, and another five before reaching 2 years of age. Sixteen of the surviving patients and the five who died between 6 months and 2 years all had psychomotor retardation. Seventeen children had structural central nervous system damage, as determined either by computed tomography or at autopsy. The extent and location of damage varied from cerebral atrophy to the development of cystic lesions in the cerebral cortex, basal ganglia, and brain stem. Two patients had ataxic episodes only and were not developmentally delayed. This cohort of patients strongly resembles a comparable group assembled from various other reports.

Acetazolamide responsive hereditary paroxysmal ataxia

The fourteenth family with an apparently autosomal dominant paroxysmal ataxia is described. As in the seven families described since 1978, acetazolamide completely cured the attacks. A possible mechanism of action of acetazolamide is discussed.

Dominant recurrent ataxia and vertigo of childhood

Four families are described with an autosomal dominant illness characterized by the childhood onset of recurrent attacks of prolonged ataxia, server vertigo, and vomiting. The attacks often begin in infancy. On the average, attacks occur monthly, and last between one hour to more than a week. Variations in severity occur within families. During an attack, consciousness is unaltered, but severe vertigo makes walking impossible and vomiting is frequent and severe. An attack is marked by horizontal and vertical jerk nystagmus, accompanied by vertigo which is sometimes worsened by position; however, there is no muscular weakness. During an attack, blood gases, ammonia, and amino acid studies are normal. Between attacks patients manifest combinations of slight horizontal or vertical jerk nystagmus or mild clumsiness. Cochlear and labyrinthine studies and neurologic investigations were noncontributory. Conventional therapies for vertigo, epilepsy, and migraine were ineffective, but acetazolamide (250-500 mg/day) stopped the attacks.

Immunochemical characterization of pyruvate dehydrogenase complex in rat brain

Pyruvate dehydrogenase complex (PDHC) in rat brain was studied immunochemically, using antibodies against the bovine kidney PDHC, by immunoblotting, immunoprecipitation, inhibition of enzyme activity, and enzyme-linked immunoabsorbent assay (ELISA). The immunoblots showed that the antibodies bound strongly to the alpha peptide of the pyruvate dehydrogenase (E1) component, and to the dihydrolipoyl transacetylase (E2) and the dihydrolipoyl dehydrogenase (E3) components of PDHC. A similar immunoblotting pattern was observed in all eight brain regions examined. On immunoblotting of the subcellular fractions, these PDHC peptides were observed in mitochondria and synaptosomes but not in the postmitochondrial supernatants. This agrees with other evidence that brain PDHC is localized in the mitochondria. These results, together with those from sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the immunoprecipitin, also showed that the alpha E1, beta E1, and E3 peptides of rat brain PDHC are very similar in sizes to those of the bovine kidney PDHC, being 42, 36, and 58 kD, respectively. The size of the E2 peptide, 66 kD, is different from that of bovine kidney E2, 73 kD. The relative abundance of PDHC protein in nonsynaptic mitochondria was compared by enzyme activity titration and ELISA. Both methods demonstrated that the amount of PDHC antigen in the mitochondria from cerebral cortex is greater than that in the olfactory bulb mitochondria. This is consistent with the results of the activity measurement. The ELISA also showed that the PDHCs in both mitochondrial populations are antigenically similar.(ABSTRACT TRUNCATED AT 250 WORDS)

Pyruvate dehydrogenase activity in regions of the rat brain during postnatal development

Activity of the pyruvate dehydrogenase complex (PDHC) was measured in seven brain regions of the male rat at various times during the postnatal period using an arylamine acetyltransferase coupled assay. Three days after birth, PDHC activity was found to be less than 15% of adult values in all brain regions with the exception of hypothalamus and medulla-pons (30% of adult values in each case). Activity of the enzyme complex in these latter regions attained adult levels by 21 days postnatally, some 5-15 days ahead of that found in cerebral cortex, striatum, hippocampus, and cerebellum. Such differences in PDHC maturation reflect the greater degree of early maturity of the phylogenetically older brain structures. Cerebellar PDHC developed more slowly than in other brain regions to attain only 40% of adult levels by the time of weaning. The pattern of maturation of cerebellar PDHC is paralleled by increased incorporation of glucose into cerebral amino acids and by the pattern of development of parallel fiber synaptogenesis. These findings suggest that PDHC may play a key role in the regional development of metabolic compartmentation and the associated maturation of cerebral function in the rat.

Familial intermittent ataxia with possible X-linked recessive inheritance. Two patients with abnormal pyruvate metabolism and a response to acetazolamide

Five males in one kindred suffered from intermittent ataxia and one female may have been more mildly affected. The pattern of inheritance strongly suggests X-linkage. Cerebral pathology in one case had some features of Leigh's disease. A defect in pyruvate metabolism was found in two cases. Acetazolamide gave a temporary clinical and biochemical improvement in two cases.

Lactic acidaemia

Congenital childhood lactic acidaemia is a poorly understood group of genetic diseases. The most common underlying inherited defect encountered in this group is deficiency of the pyruvate dehydrogenase complex. Of 23 cases we have diagnosed, 18 have a deficiency in the first component of the complex, the E1 decarboxylase, while the other five have multiple alpha-keto acid dehydrogenase deficiency due to a defect in lipoamide dehydrogenase. In addition to the lactic acidosis associated with pyruvate decarboxylase deficiency, ten of the cases showed evidence of facial dysmorphism consisting of a narrow head, wide nasal bridge and flared nostrils or gross microcephaly. Two further patients had agenesis of the corpus callosum. Isolated pyruvate carboxylase deficiency was found to present in two different forms, one with lactic acidaemia and mental retardation, the other with lactic acidaemia, hyperammonaemia citrullinaemia and hyperlysinaemia. The former presentation we have shown to be associated with the presence of a biotinylated pyruvate carboxylase protein of the correct subunit molecular weight (125 kd) which has no catalytic activity (CRM + ve). The latter we have shown to be associated with the absence of any recognizable pyruvate carboxylase protein (CRM - ve).

Decreased pyruvate dehydrogenase complex activity in Huntington and Alzheimer brain

The activity of the pyruvate dehydrogenase complex (PDHC) was reduced in affected areas of brain from patients with Huntington disease (caudate, putamen) and Alzheimer disease (frontal cortex) where choline acetyltransferase (CAT) activity was low. PDHC was also deficient in an area (Huntington hippocampus) where CAT was not significantly reduced. The activity of fumarase, an inner mitochondrial marker, was normal in all areas examined. The activities of PDHC and CAT correlated well in caudate, putamen, and amygdala but not in hippocampus or frontal cortex. Both total activity and activation of PDHC were below normal in fibroblasts from 4 patients with C-21 trisomy Down syndrome, who are at very high risk to develop Alzheimer disease. However, no abnormality of PDHC was detected in Huntington or Alzheimer fibroblasts. Deficiency of PDHC may play a role in the pathophysiology of Huntington and Alzheimer diseases, although it does not appear to be a primary defect. Loss of tissue oxidative capacity may relate to the reduction in cerebral metabolic rate and blood flow which are characteristic of many dementing illnesses.

A six-month phosphatidylcholine trial in Friedreich's ataxia

In a six-month open pilot study, pure phosphatidylcholine was administered intravenously (2.5g daily for a month) and orally (5g daily for five months) to sixteen patients with Friedreich's ataxia (FA) and seven patients with other inherited ataxias. Only the oral treatment achieved a mild but significant, 25% improvement, mainly of "central" symptoms in the FA patients at stage 2 of the illness, that is, still able to walk without support and to lead an independent life. However, the drug was ineffective in the more advanced cases. These results are discussed and compared with those obtained with lecithin by other authors.

Pyruvate dehydrogenase complex activity in normal and deficient fibroblasts

Pyruvate dehydrogenase complex (PDC) activity in human skin fibroblasts appears to be regulated by a phosphorylation-dephosphorylation mechanism, as is the case with other animal cells. The enzyme can be activated by pretreating the cells with dichloroacetate (DCA), an inhibitor of pyruvate dehydrogenase kinase, before they are disrupted for measurement of PDC activity. With such treatment, the activity reaches 5-6 nmol/min per mg of protein at 37 degrees C with fibroblasts from infants. Such values represent an activation of about 5-20-fold over those observed with untreated cells. That this assay, based on [1-(14)C]pyruvate decarboxylation, represents a valid measurement of the overall PDC reaction is shown by the dependence of (14)CO(2) production on the presence of thiamin-PP, coenzyme A (CoA), Mg(++), and NAD(+). Also, it has been shown that acetyl-CoA and (14)CO(2) are formed in a 1:1 ratio. A similar degree of activation of PDC can also be achieved by adding purified pyruvate dehydrogenase phosphatase and high concentrations of Mg(++) and Ca(++), or in some cases by adding the metal ions alone to the cell homogenate after disruption. These results strongly suggest that activation is due to dephosphorylation. Addition of NaF, which inhibits dephosphorylation, leads to almost complete loss of PDC activity. Assays of completely activated PDC were performed on two cell lines originating from patients reported to be deficient in this enzyme (Blass, J. P., J. Avigan, and B. W. Ublendorf. 1970. J. Clin. Invest. 49: 423-432; Blass, J. P., J. D. Schuman, D. S. Young, and E. Ham. 1972. J. Clin. Invest. 51: 1545-1551). Even after activation with DCA, fibroblasts from the patients showed values of only 0.1 and 0.3 nmol/min per mg of protein. A familial study of one of these patients showed that both parents exhibited activity in fully activated cells about half that of normal values, whereas cells from a sibling appeared normal. These results demonstrate the inheritance nature of PDC deficiency, and that the present assay is sufficient to detect the heterozygous carriers of the deficiency. Application of the same procedures to fibroblasts obtained from 16 individuals who were believed to have normal PDC activities showed a range from about 2-2.5 nmol/min per mg protein for adults to 5-6 nmol/min per mg protein for cells from infants.

Multiple genotypes, multiple phenotypes, and partial defects

In recent years, the following ideas have been expressed: (a) that all cases of a discrete, inherited neuromuscular syndrome should prove to be due to a single biochemical defect, (b) that any single biochemical defect should give rise only to one syndrome, and (c) that an enzymatic defect cannot give rise to a disease unless there is virtual absence of activity, that is, less than 5% or 10% of the normal value. We review evidence from research in neuromuscular, neurological, and other genetic diseases of humans that suggest the contrary. There are now examples of single clinical syndromes related to each of several defects, of defects of one biochemical reaction related to two or more distinct clinical syndromes, and of partial defects associated with disease in a way that suggests a causal relationship.

Intermittent ataxia and immunodeficiency with multiple carboxylase deficiencies: a biotin-responsive disorder

A small group of inborn errors of metabolism are manifested by intermittent cerebellar ataxia. We have previously reported a family with an inherited metabolic defect resulting in multiple carboxylase deficiencies which were responsive to pharmacological doses of biotin. Affected children presented with a skin rash, infections, acute intermittent ataxia, and lactic acidosis. Two affected siblings died prior to diagnosis and therapy, and a detailed postmortem examination was performed on one of them. The brain was characterized by atrophy restricted to the superior vermis of the cerebellum, a finding strikingly similar to that found in chronic alcoholism. Intermittent ataxia would suggest a potentially treatable metabolic disease, and clinical evaluation should include studies of intermediary metabolism and immune function.

Active pyruvate dehydrogenase in platelets from Friedreich's ataxia patients

Pyruvate dehydrogenase (PDH) activity was measured in platelets from 10 patients with Friedreich's ataxia, and 10 age-matched healthy control subjects. Both total PDH and active PDH activity were measured. There were no significant differences between the two groups.

An investigation of pyruvate metabolism in patients with cerebellar and spinocerebellar degeneration

This study extends previous observations of pyruvate metabolism in the spino-cerebellar degenerations by screening for abnormalities of pyruvate oxidation using the rise in blood pyruvate after an oral glucose load and examining the activity of the lipoamide dehydrogenase (LAD) moeity of the pyruvate dehydrogenase complex in the serum of 31 patients with Friedreich's ataxia, hereditary spastic ataxia and primary cerebellar degeneration. Serum LAD activity was significantly reduced in 10 Friedreich's ataxia patients when compared to controls and to 10 patients with spastic ataxia, thus confirming previous studies. Two patients with Friedreich's ataxia and 2 with primary cerebellar degeneration had abnormal blood pyruvate curves after oral glucose loading. The findings suggest that abnormal pyruvate oxidation occurs in some cases of Friedreich's ataxia and primary cerebellar degeneration and that the abnormality of pyruvate metabolism is not necessarily reflected in the serum LAD activity of these patients. The relevance of these findings to the heterogeneity of the hereditary ataxias is discussed.

Regulation of brain pyruvate dehydrogenase multienzyme complex

A number of excellent and comprehensive reviews on various aspects of pyruvate dehydrogenase multienzyme complex have been written recently. The purpose of the present review is to summarize briefly the reaction mechanism and the regulation of this enzyme. Emphasis is put on the most recent literature not covered by previous reviews. Particular attention is also paid to the regulation of brain pyruvate dehydrogenase multienzyme complex, since a number of patients with neuromuscular diseases, such as Friedreich's ataxia, show a decreased rate of pyruvate oxidation.

Adult-onset acid maltase deficiency: a postmortem study

In a postmortem study of a patient with adult-onset acid maltase deficiency (AMD), morphological abnormalities were confined to skeletal muscle and consisted of a vacuolar myopathy. Acid maltase activity, however, was approximately 6% of normal in muscle, liver, and brain, and 3% of normal in heart. Kinetic characteristics, and inhibition by antibodies and Zn++, showed that the residual activity was "authentic" acid maltase. Neutral maltase activity was normal in muscle and liver, but decreased in brain (55% of normal) and heart (19% of normal). Although the relative decrease of acid maltase was similar in different tissues, absolute residual activity was lowest in skeletal muscle: this may explain the selective involvement of this tissue in late-onset AMD.

Pyruvate metabolism in Friedreich's ataxia

Friedreich's ataxia patients show evidence of an abnormally elevated and prolonged response of pyruvate and lactate to a glucose load, with normal fasting levels. However, ther is a bimodal distribution of this response with high and low pyruvate responders. This trait appears to be determined genetically, However, although in vivo tests suggest low oxidation of pyruvate, we were unable to confirm any in vitro impairment of each of the components of the pyruvate dehydrogenase (PDH) complex. We conclude that the defect is in the metabolic regulation of PDH, probably at the E3 (lipoamide dehydrogenase) step.

Friedreich's ataxia 1976-an overview

The prospective investigation of 50 cases of possible Friedreich's ataxia has permitted the clinical and biochemical celineation of the typical disease and an hypothesis on its pathogenesis. A tentative definition of the disorder could read: "Friedreich's ataxia is a progressive degenerative disease always inherited in an autosomal recessive fashion and characterized by a cardiomyopathy and a ganglioneuropathy with dying back phenomenon. It is probably secondary to a defect in the membrane transport of taurine and beta-alanine and/or a defect in the regulation of pyruvate oxidation." The existence of two pathogenetically distinct distinct entities with the same phenotype is a strong possibility.