A possible genetic pattern of taurine urinary excretion in Friedreich's Ataxia

The taurine urinary excretion pattern, before and after an oral load of 250 mg taurine, was studied in normal control subjects and in patients with typical Friedreich's ataxia. It was demonstrated that in both situations the ataxic patients fell within the sub-types of "intermediate" and "high taurine excretors" while non were "low taurine excretors". It was also demonstrated that the excretion of taurine after a load in the obligate heterozygotes parents of the ataxic patients was intermediate between normal controls and patients. It is postulated that patients with Friedreich's Ataxia lack normal regulation of the high affinity-low capacity uptake system for taurine (the TH system) in the brush border of kidney tubules. The low affinity-high capacity uptake system in the same membranes (the TL system) appears to be normal in Friedreich's patients. The normal allele could be called THN and the variant THF and this trait would be inherited in an autosomal recessive fashion if it is linked to the Friedreich phenotype. Whether this finding is or is not the basic genetic defect in Friedreich's Ataxia will require more studies to clarify, but it is of interest to note that a similar pattern appears to be present in the fibroblasts of these patients.