A FIBROBLAST GLUTARYL-COA DEHYDROGENASE ASSAY USING DETRITIATION OF H-3 LABELED GLUTARYL-COA - APPLICATION IN THE GENOTYPING OF THE GLUTARYL-COA DEHYDROGENASE LOCUS

A method described earlier for measuring glutaryl-CoA dehydrogenase activity in fibroblasts has been further developed. This assay uses the detritiation of [2,3,4-H-3]glutaryl-CoA both with and without added artificial electron acceptors as a measure of glutaryl-CoA dehydrogenase activity. Fibroblasts from patients with glutaryl-CoA dehydrogenase deficiency, as determined by the (CO2)-C-14 release assay, showed very low detritiation of [2,3,4-H-3] glutaryl-CoA without added artificial electron acceptor. Obligate heterozgotes for glutaryl-CoA dehydrogenase deficiency showed detritiation activity intermediate between homozygotes and normal individuals. Addition of an electron acceptor to the assay mixture had no influence on the activity in homozygotes for glutaryl-CoA dehydrogenase deficiency but more than doubled the detritiation activity in obligate heterozygotes and in normal individuals. No difference in detritiation activity could be detected between glutaryl-CoA dehydrogenase deficient patients with a high urinary excretion of glutaric acid and patients with almost no excretion of glutaric acid. In all glutaryl-CoA dehydrogenase deficient cell lines tested the loss of decarboxylation activity was also accompanied by a loss of dehydrogenation activity. The detritiation assay was equivalent to, or even better than, the (CO2)-C-14 release assay in distinguishing between homozygotes and heterozygotes for glutaryl-CoA dehydrogenase deficiency.