Gyrate atrophy of the choroid and retina: Clinical and biochemical heterogeneity and response to vitamin B₆

Genetic heterogeneity in gyrate atrophy could reflect mutations at two separate loci, perhaps each coding for a separate subunit of the enzyme, or perhaps reflecting both structural and regulatory defects. There is no evidence to suggest the existence of more than one subunit of OAT, and the question of a regulatory defect in certain patients has not been examined. Presumably at least the patients in whom abnormal pyridoxal phosphate or ornithine kinetics were reported, all represent structural gene mutations. It seems more likely that genetic heterogeneity in gyrate atrophy reflects the occurrence of at least two mutant alleles at the locus for OAT. Our inability to demonstrate complementation in heterokaryons derived from B₆ responsive and non-responsive patients lends support to this conclusion.