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

Abnormalities of mitochondrial enzymes in hereditary ataxias

The activity of 7 mitochondrial enzymes, fumarase, NAD-malate dehydrogenase (MDH), citrate synthase (CS), valine dehydrogenase (VDH), succinate dehydrogenase (SDH), glutamate dehydrogenase (GDH), pyruvate dehydrogenase complex (PDHC) has been measured in platelet preparations from patients affected by Friedreich's ataxia (FA), dominant and non-dominant olivopontocerebellar atrophy (DOPCA, NDOPCA) and normal individuals. Significant decreases of GDH (P less than 0.01), PDHC (P less than 0.01), VDH (P less than 0.05) and SDH (P less than 0.05) activities were observed in FA patients. Significant decreases of GDH (P less than 0.01), PDHC (P less than 0.01), VDH (P less than 0.05), SDH (P less than 0.05) and CS (P less than 0.05) activities were Observed in ND-OPCA patients, whereas in DOPCA patients only GDH activity was significantly (P less than 0.05) decreased. In 8 of 10 patients with FA and in all patients with NDOPCA the activity of one or more of 4 enzymes, i.e. GDH, VDH, SDH, PDHC, was lower than the lowest of control values. Four of 6 patients with DOPCA had GDH activity lower than the lowest of control values. These results indicate that abnormalities of mitochondrial metabolism is a constant element in hereditary ataxia and suggest that the alteration primary leading to the different types of ataxias should be related to mitochondrial oxidative metabolism, at least at a regulatory level.

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).

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.

Leukocyte valine dehydrogenase activity in Friedreich's ataxia

We studied the activity of valine dehydrogenase (VDH) in leukocytes of 14 Friedreich's ataxia patients and of 14 normal control subjects. There was a significant 26% mean decrease in enzyme activity in the patients, a finding which could be responsible for the chronic accumulation of some alpha-keto acids with toxic metabolic consequences in that disease. However the deficiency was not present in all patients with the typical symptoms, nor was its magnitude sufficient to be considered the primary genetic defect in Friedreich's Ataxia.

Friedreich's disease 1982: etiologic hypotheses a personal analysis

The author reviews the arguments for and against the four etiologic hypotheses in Friedreich's disease that have been proposed since 1974: the "pyruvate hypothesis", the "lipid-membrane hypothesis", the "energy-defect hypothesis" and finally the "taurine hypothesis". While none of these hypotheses are mutually exclusive, the author shows that all of these mechanisms play some role in the pathophysiology of the symptoms, but that only the "taurine hypothesis" appears to be compatible with all the known facts and the biochemical abnormalities reported. The author proposed that the taurine retention defect (possibly due to a block in the high affinity-low capacity transport of taurine - The TH System) is a primary event in Friedreich's disease. Whether it is the primary genetic event still has to be determined.