EFFECT OF A VALINE LOAD TEST ON PLASMA ALPHA-KETO ACIDS IN FRIEDREICH ATAXIA

To test the physiological significance in vivo of a previous in vitro finding of reduced valine dehydrogenase (VDH) activity in patients with Friedreich''s ataxia, ataxic patients and controls were subjected to an oral valine load test (1.0 g) and the levels of branched chain .alpha.-keto acids were measured in the plasma for 24 h. A significantly higher peak was shown for .alpha.-keto isovaleric acid in Friedreich''s ataxia and a general trend towards higher than control values in all other .alpha.-keto acids measured. These changes are compatible with the postulated defect in regulation of the activity of VDH in this illness, but because of their small amplitude, they also indicate that a VDH-deficiency is not the genetic defect in Friedreich''s ataxia.