Detection of fabry hemizygotes and heterozygotes by the assay of specific α-galactosldase-a in single hair roots

Abstract

Fabry’s disease is an X-linked recessive disorder caused by a deficiency of lysosomal enzyme α-galactosidasc-A that results in accumulation of excess trihexosylceramide in blood vessels throughout the body which leads to corneal dystrophy, skin lesions, diffuse cardiovascular disease and renal failure. Genetic counselling requires the unequivocal identification of heterozygotes, but this is not practicable with certainty from measurement of the enzyme activity in leucocytes nor cultured skin fibroblasts. However, it has been possible to detect heterozygotes in several X-linked genetic disorders by using hair roots in which the many thousands of cells are derived from possibly single or just a few primordial cells. Therefore, and according to the Lyon hypothesis, it may be expected that a hair root would show either full normal enzyme activity, or virtually absent-mutant-activity. We have adapted our ultra-micro assay system already in use in this laboratory for detection of Hunter Syndrome heterozygotes, to the identification of Fabry carriers. The technique involves the fluorogenic assay of u -galactosidase-A (α-galactosidasc-B activity representing about 40% of the total α-galactosidase activity was inhibited by incubation in 75 nmol/l GalNAc) and the simultaneous assay (radiolabelled substrate GM 1 ganglioside) of a control enzyme activity on each of 30 50 individual hair roots. Three related hemizygotes and an unrelated fourth adult (but symptomless) hemizygote had hair root enzyme α-galactosidase-A to control enzyme ratios of virtually zero. Five female relatives of the group of three hemizygotes were studied; about 50%, of hair roots from 2 of these females showed reduced or zero activity compared to normal control subjects and their other 3 female relatives.