Friedreich ataxia: III. Mitochondrial malic enzyme deficiency

Biochemical assays of TCA cycle and β-oxidation metabolites

This chapter focuses on the methods to measure unique metabolites, specific enzymes, and metabolic flux in fatty acid β-oxidation, and on biochemical assays of tricarboxylic acid (TCA) cycle enzymes and the pyruvate dehydrogenase complex. These assays play an important role in the diagnosis of genetic diseases, newborn screening, and in cancer and metabolism research. The rationale, protocol, pros and cons, and alternative methods are discussed. Nevertheless, each laboratory should adapt the preferred method optimizing sample preparation and assay conditions for linearity and a low signal-to-noise ratio. The reader is also referred to the additional literature citing methods and clinical descriptions of the various diseases.

Cross-talk between mitochondrial malate dehydrogenase and the cytochrome bc1 complex

The interactions between the mitochondrial cytochrome bc(1) complex and matrix-soluble proteins were studied by a precipitation pulldown technique. Purified, detergent-dispersed bc(1) complex was incubated with mitochondrial matrix proteins followed by dialysis in the absence of detergent. The interacting protein(s) was co-precipitated with bc(1) complex upon centrifugation. One of the matrix proteins pulled down by bc(1) complex was identified as mitochondrial malate dehydrogenase (MDH) by matrix-assisted laser desorption ionization time-of-flight mass spectrometry and confirmed by Western blotting with anti-MDH antibody. Using a cross-linking technique, subunits I, II (core I and II), and V of the bc(1) complex were identified as the interacting sites for MDH. Incubating purified MDH with the detergent dispersed bc(1) complex results in an increase of the activities of both the bc(1) complex and MDH. The effect of the bc(1) complex on the activities of MDH is unidirectional (oxaloacetate --> malate). These results suggest that the novel cross-talk between citric acid cycle enzymes and electron transfer chain complexes might play a regulatory role in mitochondrial bioenergetics.

Friedreich ataxia: an overview

Friedreich ataxia, an autosomal recessive neurodegenerative disease, is the most common of the inherited ataxias. The recent discovery of the gene that is mutated in this condition, FRDA, has led to rapid advances in the understanding of the pathogenesis of Friedreich ataxia. About 98% of mutant alleles have an expansion of a GAA trinucleotide repeat in intron 1 of the gene. This leads to reduced levels of the protein, frataxin. There is mounting evidence to suggest that Friedreich ataxia is the result of accumulation of iron in mitochondria leading to excess production of free radicals, which then results in cellular damage and death. Currently there is no known treatment that alters the natural course of the disease. The discovery of the FRDA gene and its possible function has raised hope that rational therapeutic strategies will be developed.

Frataxin is reduced in Friedreich ataxia patients and is associated with mitochondrial membranes

Friedreich ataxia is a progressive neurodegenerative disorder caused by loss of function mutations in the frataxin gene. In order to unravel frataxin function we developed monoclonal antibodies raised against different regions of the protein. These antibodies detect a processed 18 kDa protein in various human and mouse tissues and cell lines that is severely reduced in Friedreich ataxia patients. By immunocytofluorescence and immunocytoelectron microscopy we show that frataxin is located in mitochondria, associated with the mitochondrial membranes and crests. Analysis of cellular localization of various truncated forms of frataxin expressed in cultured cells and evidence of removal of an N-terminal epitope during protein maturation demonstrated that the mitochondrial targetting sequence is encoded by the first 20 amino acids. Given the shared clinical features between Friedreich ataxia, vitamin E deficiency and some mitochondriopathies, our data suggest that a reduction in frataxin results in oxidative damage.

Regulation of mitochondrial iron accumulation by Yfh1p, a putative homolog of frataxin

The gene responsible for Friedreich's ataxia, a disease characterized by neurodegeneration and cardiomyopathy, has recently been cloned and its product designated frataxin. A gene in Saccharomyces cerevisiae was characterized whose predicted protein product has high sequence similarity to the human frataxin protein. The yeast gene (yeast frataxin homolog, YFH1) encodes a mitochondrial protein involved in iron homeostasis and respiratory function. Human frataxin also was shown to be a mitochondrial protein. Characterizing the mechanism by which YFH1 regulates iron homeostasis in yeast may help to define the pathologic process leading to cell damage in Friedreich's ataxia.

Correlation between left ventricular hypertrophy and GAA trinucleotide repeat length in Friedreich's ataxia

BACKGROUND

Friedreich's ataxia (FA), the most common inherited ataxia, is associated frequently with cardiac hypertrophy, and death is often cardiac related. Recently, the disease has been associated with a mutation that consists of an unstable expansion of GAA repeats in the first intron of the gene encoding frataxin on chromosome 9.

METHODS AND RESULTS

We studied 44 consecutive patients with FA, determined the size of GAA expansions in the frataxin gene, and examined the relation between the genotype and cardiac phenotype assessed by M-mode and two-dimensional echocardiography. All the patients were homozygous for the mutation. The size of the GAA expansion on the smaller allele varied from 270 to 1200. We found a correlation between the size of GAA expansion and the left ventricular wall thickness (r = .51, P < .001) and the left ventricular mass index (r = .45, P = .002). Left ventricular hypertrophy was observed in 81% of patients with a number of GAA repeats above the median value of 770 compared with only 14% in the other group (P = .002).

CONCLUSIONS

These data demonstrate that in FA, the severity of left ventricular hypertrophy is related to the number of GAA repeats. These results suggest that abnormalities of the gene encoding frataxin, a protein of unknown function highly expressed in the normal heart, may play an important role in the modulation of cardiac hypertrophy.

Heart disease in Friedreich's ataxia: a clinical and echocardiographic study

Twelve patients with Friedreich's ataxia (FA) were evaluated clinically and echocardiographically for evidence of heart disease. Electrocardiographic and echocardiographic abnormal findings were discovered in eight (67%) and seven (58%) children, respectively. A high incidence of cardiac involvement is well known in FA cases. Although the patient number in the present study is small, the findings are consistent with those in the literature. The most common pathology was asymmetric septal hypertrophy (ASH), followed by concentric left ventricular hypertrophy (CLVH) and dilated cardiomyopathy (DC).

Cloning, sequencing and functional expression of a cDNA encoding a NADP-dependent malic enzyme from human liver

This work reports the structure of a cDNA (ME) encoding a human malic enzyme (ME) (malate NADP oxidoreductase, EC 1.1.1.40) elucidated by joining several overlapping fragments amplified by PCR from human hepatic cDNA or from cDNA libraries. The full-length cDNA has an open reading frame (ORF) of 1719 bp that encodes a 572-amino-acid protein of 64 113 Da, similar to the native monomeric, cytosolic, NADP-dependent ME isolated from human liver. The comparison of the structure of this cDNA with that of the human mitochondrial NAD(P)-dependent ME (EC 1.1.1.39) shows a homology of 63%, suggesting that these two forms originated from the same gene. The expression of the cDNA in Escherichia coli as a translational fusion (glutathione S-transferase::ME) protein yielded a product of the predicted mass. The recombinant protein shows NADP-dependent malate oxidoreductase activity and is virtually inactive with NAD. It also shows other distinct features of the native cytosolic NADP-dependent ME, like Mn2+ dependence, similar substrate (Km = 117 microM) and cofactor affinity (Km = 2 microM) constants, and a lack of allosteric regulation. In human proliferative cells, the NADP-dependent ME activity is poorly expressed and barely inducible by thyroid hormones.

The clinical spectrum of Friedreich's ataxia in German families showing linkage to the FRDA locus on chromosome 9

The clinical features of Friedreich's ataxia are described and reevaluated in a group of 14 German patients from 9 independent families. In contrast to previous studies, demonstration of linkage to the Friedreich's ataxia locus (FRDA) on chromosome 9p allowed confirmation of the genetic homogeneity of the disease in the patients under study. Marked variability within families was observed for age of onset of the disease (4-24 years) and for age of becoming wheelchair bound (17-37 years). Electrocardiographic changes were present in all and echocardiographic changes in 50% of the patients. Pathological changes of visual evoked potentials were detected in only 50% of the patients while brainstem auditory evoked potentials and somatosensory evoked potentials were always abnormal.

Human malic enzymes in heart and muscle: evidence of a selective distribution

The NADP(+)-dependent activity of malic enzymes EC 1.1.1.39 and EC 1.1.1.40 was studied in human cardiac and skeletal muscle obtained from living subjects. We used polyacrylamide gel electrophoresis to detect and extract the enzymatic forms and starch gel electrophoresis to confirm their identification. This simple procedure allowed us to provide evidence of a selective NADP(+)-dependent distribution of malic enzyme activities between the two muscular tissues, using a smaller amount of sample than used with previous methods.

Cerebral glucose hypermetabolism in Friedreich's ataxia detected with positron emission tomography

Local cerebral metabolic rate for glucose was studied with 18F-2-fluoro-2-deoxy-D-glucose and positron emission tomography (PET) in 22 patients with Friedreich's ataxia and 23 age-matched normal control subjects. The diagnosis of Friedreich's ataxia was established by the history and physical findings and by excluding other diseases through laboratory investigations. PET studies revealed a statistically significant widespread increase of local cerebral metabolic rate for glucose in the brains of patients with Friedreich's ataxia who were still ambulatory, in comparison with normal control subjects. Nonambulatory patients with Friedreich's ataxia, in comparison with normal control subjects, had significantly increased local cerebral metabolic rates for glucose in the caudate and lenticular nuclei, but not in the other structures studied. The rate was significantly greater in ambulatory patients with Friedreich's ataxia than in nonambulatory patients in all structures studied except the caudate and lenticular nuclei. The data suggest that early in the course of Friedreich's ataxia, the local cerebral metabolic rate for glucose is increased extensively in the central nervous system, and as the disease progresses, it decreases in a regionally specific manner.

The nosologic panorama of progressive ataxia in Swedish children

Described are 76 children with a picture of progressive encephalopathy and ataxia as the principal or joint principal leading signs. The series was hospital-based in Gothenburg between 1973 and 1983, and not representative for epidemiologic analyses. The children were divided in groups by using a combined pathogenetic and clinical grouping system: lysosomal disorders (6 children), non-lysosomal lipid disorders (10), intermediary metabolic disorders (3), heredoataxias (22), phacomatoses including Louis-Bar (5), dysimmune encephalopathies (6), other defined disorders (19) and undefined or incompletely defined conditions (5). Different groups are discussed and, according to this material, a diagnostic pathway is drawn up.

Mitochondrial enzymes in hereditary ataxias

As a test of the hypothesis that mitochondrial abnormalities are common in patients with hereditary ataxias, the activities of two mitochondrial enzymes were studied in platelets from an unselected series of patients. For the group of ataxics, the activity of the pyruvate dehydrogenase complex (PDHC) was 68% of the control (P less than 0.01) and that of glutamate dehydrogenase (GDH) was 81% of the control (P less than 0.05). Of the ataxics studied, 30% had activities of either or both mitochondrial enzymes more than 2 SD below the control mean. Immunoblots of PDHC revealed antibody cross-reacting material in platelets and fibroblasts very similar to those in human brain and appeared normal in platelets from patients with ataxias. Immunoblots of GDH showed a single antibody cross-reacting material in brain but at least two species in normal fibroblasts and platelets. The pathophysiology of hereditary ataxias may often involve mitochondrial damage associated with secondary decreases in the activities of mitochondrial enzymes.

Purification and properties of cytosolic malic enzyme from human skeletal muscle

1. An NADP+-dependent malic enzyme was purified 7940-fold from the cytosolic fraction of human skeletal muscle with a final yield of 55.8% and a specific activity of 38.91 units/mg of protein. 2. The purification to homogeneity was achieved by ammonium sulfate fractionation, DEAE-Sepharose chromatography, affinity chromatography on NADP+-Agarose, gel filtration on Sephacryl S-300 and rechromatography on the affinity column. 3. Either Mn2+ or Mg2+ was required for activity: the pH optima with Mn2+ and Mg2+ were 8.1 and 7.5, respectively. The enzyme showed Michaelis-Menten kinetics. At pH 7.5 the apparent Km values with Mn2+ and Mg2+ for L-malate and NADP+ were 0.246 mM and 5.8 microM, and 0.304 mM and 5.8 microM, respectively. The Km values with Mn2+ for pyruvate, NADPH and bicarbonate were 8.6 mM, 6.1 microM and 22.2 mM, respectively. 4. The enzyme was also able to decarboxylate malate in the presence of NAD+. At pH 7.5 the reaction rate was approximately 10% of the rate in the presence of NADP+, with a Km value for NAD+ of 13.9 mM. 5. The following physical parameters were established: s0(20.w) = 10.48, Stokes' radius = 5.61 nm, pI = 5.72 Mr of the dissociated enzyme = 61,800. The estimates of the native apparent Mr yielded a value of 313,000 upon gel filtration, and 255,400 with f/fo = 1.33 by combining the chromatographic data with the sedimentation measurements. 6. The electron microscopy analysis of the uranyl acetate-stained enzyme revealed a tetrameric structure. 7. Investigations to detect sugar moieties indicated that the enzyme contains carbohydrate side chains, a property not previously reported for any other malic enzyme.

Evidence for two distinct mitochondrial malic enzymes in human skeletal muscle: purification and properties of the NAD(P)+-dependent enzyme

Human muscle mitochondria reduced either NADP+ or NAD+ in the presence of L-malate and Mn2+ or Mg2+. After polyacrylamide slab gel electrophoresis and agarose gel isoelectrofocusing, two bands were seen in mitochondrial extract, one strictly NADP+-dependent and the other reacting with either NAD+ or NADP+. The two mitochondrial malic enzymes were separated by DEAE-Sepharose chromatography. The NAD+/NADP+-dependent enzyme was purified 1600-fold with a final yield of 34% and a final specific activity of 32.9 units/mg of protein by employing affinity chromatography on Agarose-ATP. SDS electrophoresis revealed a single band having an apparent Mr = 64,000. Estimates of the native apparent molecular weight upon gel filtration yielded a value of 140,300. Kinetic characterization showed that succinate and ATP were activator and inhibitor, respectively. In the absence of succinate the Km values for malate, NAD+ and NADP+ were 3.7, 0.13 and 0.78 mM, respectively; in the presence of succinate the Km value for malate was 1.9 mM. ATP was found to be an inhibitor competitive with malate, with a Ki (ATP) of 0.2 mM. This is the first report to show that mammalian skeletal muscle mitochondria contains two distinct malic enzymes, one active with either NAD+ or NADP+ and the other active only with NADP+.

Mitochondrial hydroxyapatite deposits in spinocerebellar degeneration

We report the presence of crystalline deposits of calcium hydroxyapatite in the mitochondria of 2 children with sporadic spinocerebellar degeneration. The deposits, identified by electron microscopy, were found in the mitochondria of neurons and smooth muscle cells in one patient and in only smooth muscle cells in the second child, but not in other cell types. The calcific nature of the deposits was confirmed by laser microprobe mass analysis. The calcium overload may interfere with mitochondrial function, as has been shown in the cardiomyopathic strain of the Syrian hamster, a model of the cardiomyopathy of Friedreich's ataxia.

Friedreich's ataxia: electrophysiologic and histologic findings in patients and relatives

Peripheral nerve conduction velocity and cortical evoked potentials were investigated in 48 patients with Friedreich's disease and in 35 relatives. There were 14 patients and 2 relatives who underwent sural nerve biopsy. In the patients sensory conduction velocity was moderately slowed, whereas sensory responses were markedly reduced. Nerve biopsy showed a severe loss of large myelinated fibers and no demyelination. On teased nerve fiber preparations, most fibers presented uniformly short internodes. No correlation was seen between sensory conduction findings or histologic abnormalities and clinical disability. In patients SSEP changes, which were constant, and VEPs, which were frequently involved, were unrelated to the severity or duration of clinical disability. There were 14 relatives who showed clinical signs of Friedreich's disease. Slightly decreased distal conduction velocity along sensory fibers was observed in more than half of the relatives. Nerve biopsy was noncontributory. In conclusion, we could not determine whether the abnormalities observed in the siblings were an expression of a heterozygotic condition, or whether they were early signs of the disease.

Exclusion of the Friedreich ataxia gene from chromosome 19

Friedreich ataxia, a progressive neurodegenerative disorder, is an autosomal recessive disease with a carrier frequency of 1/110 in the United Kingdom. The pathophysiological basis for the disease is not known and the chromosomal location of the mutation remains unidentified. As part of an attempt to map the mutation using linked DNA markers, we demonstrate that the Friedreich ataxia gene is excluded from human chromosome 19. This study also demonstrates that the insulin receptor, which maps to chromosome 19 and may be associated with abnormal biochemical features in some patients, is not the basic defect.

Morphologic and functional characteristics of the heart in Friedreich's ataxia

The purpose of this study was to characterize the heart in patients with Friedreich's ataxia by two-dimensional echocardiography, systolic time intervals, and heart biopsy. Ten patients with Friedreich's ataxia (seven females and three males, age 15 +/- 7 years) were compared with 10 age-matched normal subjects (five males and five females, age 16 +/- 7 years). The mean systolic blood pressure in the patients with Friedreich's ataxia was lower (114 +/- 9 mm Hg) than that in the control subjects (122 +/- 8 mm Hg; p less than 0.05); diastolic blood pressures were the same. The heart rate in the patients with Friedreich's ataxia (102 +/- 17 beats/minute) was greater than that in the control subjects (76 +/- 12 beats/minute; p less than 0.001). The interventricular septal wall thickness was much greater in Friedreich's ataxia (13 +/- 2 versus 8 +/- 1 mm, p less than 0.001) as was the posterior wall thickness (13 +/- 3 versus 8 +/- 1 mm, p less than 0.001). The left ventricular end-diastolic diameter was smaller in Friedreich's ataxia (35 +/- 6 mm versus 47 +/- 6 mm; p less than 0.01), and the fractional change of the left ventricular minor axis with systole was greater in Friedreich's ataxia (40 +/- 9 percent versus 33 +/- 5 percent; p less than 0.05). An 11th patient with Friedreich's ataxia (age 33) had clinical heart failure, but his course was complicated by alcohol abuse. Heart biopsy in three patients with Friedreich's ataxia demonstrated myocyte hypertrophy (21.5 +/- 2.0 microns diameter; normal, 14 to 17 microns) and increased fibrosis (16 +/- 9 percent; normal, less than 5 percent). Thus, heart disease in Friedreich's ataxia is characterized by myocyte hypertrophy, interstitial fibrosis, increased left ventricular wall thickness, decreased left ventricular cavity size, sinus tachycardia, and normal systolic function. Further biochemical analysis of tissues may lead to the link of the neurologic and cardiac diseases and eventually to more effective therapy of this condition.

Cardiac involvement in Friedreich's ataxia: a clinical study of 75 patients

To establish the prevalence and to characterize the types of cardiac involvement in Friedreich's ataxia, 75 consecutive patients (39 male and 36 female), aged 10 to 66 years (mean 24) were prospectively studied. Electrocardiograms were performed in all patients, vectorcardiograms in 34 and echocardiograms in 58. Electrocardiographic and vectorcardiographic abnormalities occurred in 69 (92%) of the 75 patients. Electrocardiograms revealed ST-T wave abnormalities in 79%, right axis deviation in 40%, short PR interval in 24%, abnormal R wave in lead V1 in 20%, abnormal inferolateral Q waves in 14% and left ventricular hypertrophy (voltage and repolarization criteria) in 16%. Echocardiograms revealed concentric left ventricular hypertrophy in 11%, asymmetric septal hypertrophy in 9% and globally decreased left ventricular function in 7%. Progression from a normal echocardiogram to concentric left ventricular hypertrophy, asymmetric septal hypertrophy or globally decreased left ventricular function was identified in one patient in each category, although the study was not designed for longitudinal follow-up. Two patients died, and necropsy revealed in both a minimally dilated but flabby left ventricle. On the basis of electrocardiographic and vectorcardiographic and echocardiographic data, 95% of patients had one or more disorders. The most common abnormality was segmental myocardial "dystrophy" (electrocardiographic QRS initial force abnormalities), but global left ventricular hypokinesia occurred more often than previously recognized.(ABSTRACT TRUNCATED AT 250 WORDS)

Mitochondrial abnormalities in fibroblast line GM3093 defective in oxidative metabolism

Fibroblast line GM3093 deficient in the activity of the pyruvate dehydrogenase complex, was derived from a patient reported to have an inherited defect affecting the tricarboxylic acid cycle. Our results suggest a generalized defect consisting of few and abnormal mitochondria and low activities of all mitochondrial enzymes examined.

Mitochondrial dysfunction and spinocerebellar degenerations

A simplified classification of the spinocerebellar degenerations is proposed. Axonal ataxias include Friedreich's ataxia and other conditions involving, primarily, neurons with very long axons. Multiple system degenerations include the various olivopontocerebellar atrophies and related disorders. Ataxic encephalopathies are diffuse diseases of the nervous system in which ataxia is a prominent clinical feature. Several lines of data suggest that mitochondrial damage is a common mechanism in the spinocerebellar degenerations. Reasonable pathophysiological mechanisms can be invoked, linking mitochondrial damage to the observed pathologies (including the many cases of intermediate on variant forms).

Alzheimer's disease. A metabolic systems degeneration?

Alzheimer's disease can be considered a late-onset system degeneration, characteristically involving certain populations of cholinergic neurons but eventually involving other cells as well. Decreases in cerebral metabolic rate occur in it and may reflect not only decreased neuronal activity, but also deficiencies in metabolic enzymes. Abnormalities reported in nonneural Alzheimer tissues suggest that at the molecular level it is a systemic disease whose biochemical aspects can usefully be studied in nonneural tissues. Alzheimer's disease can be formulated as one of a number of metabolic encephalopathies that impair central cholinergic function.

Enzymatic analysis of individual posterior root ganglion cells in olivopontocerebellar atrophy, amyotrophic lateral sclerosis and Duchenne muscular dystrophy

Four enzyme activities related to glucose metabolism, i.e. those of glucose-6-phosphate dehydrogenase (G6PDH; EC 1.1.1.49), lactic dehydrogenase (LDH; EC 1.1.1.27), pyruvate dehydrogenase complex (PDC) and citrate synthase (CS; EC 4.1.3.7) were estimated in posterior root ganglion cells (PRGCs) of the spinal cord in patients suffering from olivopontocerebellar atrophy (OPCA), amyotrophic lateral sclerosis (ALS), and Duchenne muscular dystrophy (DMD) by means of the NAD, NADP and CoA cycling methods. In ALS and DMD, the enzyme activities examined were within normal ranges. In OPCA, PDC activity was significantly reduced and LDH activity tended to be lower than that in controls.

The inherited ataxias

Clinical, biochemical, and genetic studies have brought clarity to many issues concerning the inherited ataxias. The classification, diagnosis, and therapy of hereditary ataxias are now better understood although many questions remain. Basic defects are identified in some disorders.

Electrocardiographic abnormalities in pediatric neuromuscular disease: a review

Cardiac abnormalities, often heralded by electrocardiographic alterations, at times may become a serious problem in patients with neuromuscular disorders and occasionally lead to death. Electrocardiographic monitoring can identify patients whose conduction defects will benefit from the use of demand pacemakers.

Brainstem auditory-evoked responses and clinical picture in a one year follow-up of 18 patients with Friedreich ataxia

Brainstem auditory-evoked responses (BAER) and behavior audiometry were evaluated on 18 patients with Friedreich ataxia. Behavior audiometry showed a normal pure tone test, normal performance intensity and phonetically balanced functions in all patients. BAER were abnormal in all patients. The data obtained show a good correlation between BAER and clinical picture and suggest that BAER could be useful in monitoring the clinical condition of FA patients.

Mitochondrial malic enzyme in Friedreich's ataxia: failure to demonstrate reduced activity in cultured fibroblasts

Mitochondrial and cytosolic malic enzymes were assayed radiochemically in fibroblasts from six patients suffering from Friedreich's ataxia in order to verify earlier reports of abnormalities in these enzymes. No abnormalities could be detected in the activities of either enzyme. On cellulose acetate electrophoresis a band of enzyme activity corresponding to the mitochondrial isoenzyme was detectable contrary to earlier reports. Possible explanations for the disparity of results between different laboratories are discussed.

Cardiac malic enzyme in Friedreich's disease

We measured the activity of cytosolic and of mitochondrial malic enzyme in the hearts from 4 patients with Friedreich's disease and from two non-ataxic control subjects. There was a wide variability in the results and the slight overall decreases in both enzyme activities were not considered to be statistically significant. From these and other results, we conclude that deficient mitochondrial malic enzyme activity is not a constant or primary feature of Friedreich's disease.

Friedreich's ataxia: malic enzyme activity in cellular fractions of cultured skin fibroblasts

We have measured the activity of malic enzyme NADP+ dependent in the nuclear, mitochondrial, lysosomal and cytosolic fractions of cultured skin fibroblasts from twelve patients with Friedreich's ataxia and nine control subjects. Hexosaminidase, cytochrome-C-oxidase, lactate dehydrogenase and malic enzyme NAD+ dependent were used as marker enzymes. The activity of malic enzyme NADP+ dependent was not significantly reduced in the mitochondrial fraction of patients with Friedreich's ataxia as compared with controls. When corrected for possible contamination between mitochondrial and cytosolic fractions, malic enzyme NADP+ dependent activity was still not significantly reduced in patients with Friedreich's ataxia. Unless critical methodological differences were overlooked in this or previously published studies, we conclude that mitochondrial malic enzyme deficiency is not the primary genetic defect underlying Friedreich's ataxia.

The Quebec Cooperative Study of Friedreich's Ataxia: 1974-1984--10 years of research

In this paper the author reviews the progress accomplished in the understanding of Friedreich's disease since the start of the "Quebec Cooperative Study of Friedreich's Ataxia" in 1974. The last ten years have indeed seen important strides taken in the definition and nosography of the hereditary ataxias and the characterization of a number of new entities. Biochemically, the principal leads uncovered during the initial prospective survey, have been pursued to great detail. Unfortunately no clear-cut constant and severe enzyme block in the principal metabolic pathways has yet been identified, despite intensive studies. It is postulated that the defect may instead be a regulatory one and involve a decreased availability or utilization of one of the vitamin cofactors that are known experimentally, or clinically, to produce central nervous system damage with ataxia: Vitamin E, Biotin or Pantothenic Acid. Studies in that direction and in molecular genetics to localize the Friedreich's disease gene are being undertaken for the next phase of the Cooperative Study.

A microchamber for polarographic assay

A glass micro-chamber which allows polarographic assay in a volume of 180 microliter is described. The conical shape of this chamber allows efficient mixing with a Teflon magnetic flea. This chamber facilitates the study of the small quantities of mitochondria obtained from human tissue biopsies or animal sources. The polarographic assay of mouse liver mitochondria is described.

Induction of the morphologic changes of both acute and chronic experimental myasthenia by monoclonal antibody directed against acetylcholine receptor

To investigate pathogenic mechanisms in experimental autoimmune myasthenia gravis (EAMG) and myasthenia gravis (MG), we studied the acute and chronic effects in rats of injection of rat monoclonal antibodies ( MCABs ) directed against the acetylcholine receptor (AChR). Animals were severely weak 12 h after a single injection, at which time macrophages were found invading endplate regions of muscle and cholinesterase-stained regions were separted from the underlying muscle fibers. Ultrastructural studies showed findings identical to the acute phase of EAMG: degenerating postsynaptic membranes and invasion and phagocytosis of endplate regions by macrophages. Animals receiving sublethal doses of MCAB recovered clinically by 4-5 days after injection. Recovery was accompanied by a progressive decrease in the number of macrophages associated with endplates and reapposition to the myofibers of the cholinesterase-stained regions. Animals injected once, or repeatedly over several months, remained clinically and electromyographically normal after recovery from the initial episode of weakness, but their endplate ultrastructure was highly simplified with blunted or absent synaptic folds and shallow or absent secondary synaptic clefts. These studies demonstrate that anti-AChR MCABs can induce the changes of both acute and chronic EAMG. There is good correlation between the inflammatory changes and the acute clinical disease but poor correlation between morphological and clinical parameters in the chronic syndrome. The latter observation suggests that severe ultrastructural changes, similar to those seen in chronic EAMG and MG, cannot account, at least in rats, for the clinical and electrophysiologic abnormalities of MG.

Review: the cerebrohepatorenal syndrome of Zellweger, morphologic and metabolic aspects

The cerebrohepatorenal syndrome of Zellweger (CHRS) is remarkable not only for a distinctive combination of congenital anomalies, but also for an unusual variety of profound metabolic disturbances. After a discussion of the clinical diagnosis of CHRS, abnormalities in the metabolism of peroxisomes, mitochondria, iron, pipecolic acid, glycogen, bile acids, and organic acids are discussed and related to the clinical and other biochemical findings in the syndrome. Attention is also drawn to syndromes with biochemical or clinical abnormalities similar to those of CHRS. Although the biochemical findings indicate major abnormalities in oxidative metabolism, the primary defect remains obscure.

Normal mitochondrial malic enzyme levels in Friedreich's ataxia fibroblasts

Normal levels of mitochondrial malic enzyme were found in fibroblasts from three patients with Friedreich's ataxia.

Neurodegenerative diseases of infancy and childhood

The neurodegenerative diseases of infancy and childhood include disorders in which there is progressive loss of neurological function due to structural abnormalities of the central nervous system. Well over six hundred disorders, many of which are rarely seen, can be included in this category. Yet, the conditions represent collectively over one-fourth of all admissions to pediatric neurology services. Five-year samples of admission characteristics of 1218 patients from two medical centers over twenty-two years permit an estimate of the frequency of the neurodegenerative diseases. The six most-encountered diagnoses, in declining order, were: subacute sclerosing panencephalitis; neuronal ceroid lipofuscinosis; tuberous sclerosis with degeneration; West disease, or idiopathic degenerative encephalopathy associated with infantile spasms; Werdnig-Hoffmann disease, and hereditary spastic paraplegia. A classification is offered grouping the neurodegenerative disorders into five major categories: polioencephalopathies, leukoencephalopathies, corencephalopathies, spinocerebellopathies, and diffuse encephalopathies. Disorders in each subgroup may be either genetic or nongenetic. Neurodegenerative diseases have multiple causes, including metabolic, viral, immunopathic, environmental, and epileptogenic. The cause of many remains unknown.

Friedreich ataxia and low pyruvate carboxylase activity in liver and fibroblasts

Biochemical studies in liver, muscle, and cultured fibroblasts were carried out in seven patients with Friedreich ataxia. Lowered activity of pyruvate carboxylase was shown in liver and cultured fibroblasts in all instances.

Hypertrophic cardiomyopathy is a component of subacute necrotizing encephalomyelopathy

Twelve patients, ranging from the neonatal period through adolescence, with subacute necrotizing encephalomyelopathy (Leigh disease) were studied. Autopsies of these patients demonstrated an associated hypertrophic cardiomyopathy in seven; of these, four had asymmetric septal hypertrophy. In two patients, the cardiac lesion was observed by premortem echocardiograms. The common occurrence of a cardiac lesion emphasizes the probable systemic nature of SNEM and may serve to segregate these patients into two groups. Because of the involvement of the two systems, we suggest that SNEM may have some relation to a variety of other cardioneurologic syndromes.