Homozygotes, obligatory heterozygotes and potential carriers of the Friedreich's Ataxia gene were tested with an oral glucose tolerance in order to assess a. the prevalence of abnormalities in glucose handling, b. the secretory pattern of two “diabetogenic” hormones, growth hormones and prolactin and c. to evaluate the possibility for detection of an abnormal trend in these hormones to be used as a genetic marker. Despite the high prevalence of glucose abnormalities horizontally and vertically in these families, the basal output and responses of these metabolic hormones to a glucose challenge were appropriate and thus not characteristic of any of the above groups.

In a study of glycosylated hemoglobins in Friedreich's Ataxia patients and in family members, the level was found to be higher in insulin dependent diabetics than in healthy non-diabetic control subjects (p<0.01), but was similar to non-ataxic diabetic control subjects. Results for non-diabetic Friedreich's Ataxia patients and siblings were similar to those for non-diabetic control subjects while levels were slightly increased in the heterozygotes. It is concluded that in Friedreich's Ataxia patients and family members (apart from the insulin dependent diabetics), there was no hyperglycemia sufficient to be detected as an increase in glycosylated hemoglobins.

Pyruvate and palmitate oxidations by cultured fibroblasts suspensions were measured in optimized conditions and proved to be within normal range in the cells from Friedreich's patients. However, when pyruvate oxidation was measured by direct assay of the pyruvate dehydrogenase complex, this enzyme activity proved to be significantly lower in Friedreich's than in controls' cells. These abnormalities were not observed when the cells were sonicated. Moreover, lipoamide dehydrogenase activity. Km and Vmax were within the normal range in Friedreich 's cells. These data suggest that the low activities of the PDH complex are not a primary defect in Friedreich's ataxia, but are more likely related lo membrane abnormalities in Friedreich's cells.

Serum lipoamide dehydrogenase activity and kinetics were studied in nine patients with Friedreich's ataxia before and three months after therapy with oral lecithin. Results disclosed a significant reduction in LAD inhibition by NADH in all patients after therapy. Three patients normalized their increased Km for lipoamide and one patient showed the opposite results after therapy. Two patients ceased lecithin after one month. All seven patients who remained in the trial group and one additional patient, showed subjective and objective signs of improvement in physical resistance. This study has offered some biochemical basis for the apparent clinical improvement in patients with Friedreich's ataxia who undergo lecithin therapy.

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.

Leucocyte Glutamate Dehydrogenase (GDH) activity was measured in 44 patients with various forms of ataxia and 44 age and sex-matched normal controls. The only significant change found was a moderate decrease in activity in Freidreich's ataxia and a few patients with OPCA. This decreased activity is not primary to the disease but probably reflects a regulatory defect affecting mitochondrial membranes in these patients.

Proteins of human erythrocyte membranes of Friedrich's ataxia patients and controls were examined by SDS-polyacrylamide gel electrophoresis before and after reduction withβ-mercaptoethanol. No difference could be detected in the composition of their state of aggregation. The protein kinase activity of human erythrocyte membranes of eleven Friedreich's ataxia patients and six controls was determined. No difference in their protein kinase activity could be detected. These results are discussed with respect to an involvement of a generalized membrane defect in Friedreich's ataxia.

In a study of the fatty acid composition of erythrocyte membrane phospholipids in Friedreich's ataxia, a lower percentage of linoleic acid in phosphatidylcholine was demonstrated. An enzyme involving the exchange of lipids between plasma and erythrocyte membrane, lecithin: cholesteryl acyltransferase (LCAT) was also studied. It was found that the LCA Tactivity had a trend towards low values. However, crossing-over studies indicated that when the LCAT enzyme of patients was exposed to its own substrate it gave low activity values but that the result reverted to normal when control substrate was used

Cardiomyopathic Syrian hamsters develop necrotic lesions consequent upon calcium overload from 60 days of age onward. Taurine, given as a 0.1M solution in place of drinking water for one month prior to sacrifice of animals of initial age 35 days, decreased the severity of subsequently developing cardiac lesions by 40%. Calcium concentration in the heart was decreased by 57%. Magnesium and iron concentrations were unaltered. Taurine given in a similar manner for 4 months had a protective effect, decreasing lesion severity by 21% and calcium concentration by 35%. Magnesium concentrations were increased by 12%. Compared to randombred animals, cardiomyopathic hamsters at one and two months of age have the same concentrations of calcium, magnesium and iron in the quadrants of the heart, except in the left ventricle, which has significantly higher concentration of calcium. Calcium concentrations are 70%, 1320% and 2100% higher respectively in one month, two month and five month old animals. Five month old animals differ slightly but significantly in iron (17% decrease) and magnesium concentrations (17% increase).

Cardiomyopathic hamsters have insignificant differences in β-adrenergic receptor density compared to random-bred animals and have a significantly higher rate of taurine influx.

Taurine and β-amino uptake in cultured skin fibroblasts proceeds through at least two distinct amino acid transport systems. The predominant Bamino acid uptake system which we refer to as the “Beta” system, incorporates taurine in a proportion of 95%, β-alanine in a proportion of 80% and does not incorporate β-amino-isobutyric acid. A second transport system for β-alanine seems to be operative in cultured skin fibroblasts and this system shares the characteristics of system “L” for branched-chain and ringside neutral amino acids. Results of ion depletion experiments, metabolic inhibition by drugs and blocking agents and previous kinetic studies of taurine and β-alanine uptake in cultured skin fibroblasts failed to disclose any major difference in β-amino acid transport between control individuals and patients with Friedreich's ataxia.

Treatment of rats with asparagine or glutamine caused substantial increases in glutamine concentrations in cerebellum and medulla oblongata. Insulin treatment caused a diminution of glutamate and GA BA in these regions of brain. Since it is now well-established that glutamine is a very efficient precursor of the neurotransmitter pool of glutamate in mammalian brain, treatment with asparagine or glutamine could be of therapeutic (replacement) value in the treatment of neurological disorders such as Friedreich's ataxia, in which cerebral glutamate concentrations have been found to be diminished.

The main purpose of this study was to examine the effects of intraventricular injections of glutamate and aspartate on the walking gait of rendered ataxic by the administration of 3-acetyl pyridine. Both amino acids significantly improved the walking gait of these animals. The effects of other substances known to have a stimulatory influence on locomotor activity in rats were also investigated. Amphetamine, apomorphine and thyrotropin releasing hormone (TRH) had no effect on the ataxic gait of 3-AP treated animals. Substance P significantly improved the gait of ataxic animals, but to a lesser extent than that seen with glutamate and aspartate.

Phase three of the Quebec Cooperative Study of Friedreich's Ataxia was devoted to an understanding of the physiopathology of individual symptoms on the basis of previously discovered biochemical leads. The present paper attempts to pull these results together by presenting, as a hypothesis, a unifying scheme of possible interactions and relationships. The central core of this hypothesis is the demonstration in Friedreich's ataxia of a state of mitochondrial energy deprivation. This is indirectly responsible for such associated and important symptoms as muscle weakness, dying-back neuropathy, scoliosis and hypertrophic cardiomyopathy. Secondarily, and possibly as an independent but linkedevent, the entry of glucose into cells and pyruvate oxidation, are slowed down, favoring the development of diabetes. As a consequence, tissue concentrations of glutamic acid and aspartic acid are decreased, particularly in more vulnerable areas such as the cerebellum, brain stem and dorsal root ganglia. This tissue deficiency in putative excitatory neurotransmitters is directly responsible for the symptom of ataxia. This conclusion is reinforced by the correction of the ataxia in glutaexperimental animals, by the intraventricular injection of the same amino acids, and not by the injection of other stimulants of motricity. The observed mitochondrial energy deprivation could be the metabolic consequence of major changes in the linoleic acid (18:2) composition of inner mitochondrial membrane phospholipids, such as cardiolipin. Such decreases in membrane 18:2 could be the result of interference with the normal incorporation of this fatty acid to lipoproteins and/or cell membranes. It is at this level that the search for the specific enzyme defect in Friedreich's ataxia is continuing.