Fabry disease in a large Nova Scotia kindred: carrier detection using leucocyte alpha-galactosidase activity and an NcoI polymorphism detected by an alpha-galactosidase cDNA clone.

Fabry disease is an X linked recessive disorder of glycosphingolipid metabolism resulting from a deficiency of the lysosomal hydrolase alpha-galactosidase (alpha-gal). Measurement of the enzyme activity, however, is not an accurate method for identification of female carriers among at risk relatives of affected males. The alpha-gal cDNA and gene have been cloned previously and found to provide useful probes for the molecular analysis of affected families but these clones have not been available to us. Thus, to analyse Fabry disease in Nova Scotia, especially within a large kindred known to contain 30 affected males and 50 possible carrier females, we isolated an independent cDNA for alpha-gal. Using this clone as a probe, the mutation in the Nova Scotia kindred was shown not to be a major DNA alteration, but was found to be linked to the rarer allele (frequency 0.20) of the polymorphic NcoI site located 3' to the gene. Affected males from two Nova Scotia families who cannot be associated with the kindred by history were also found to have the rarer NcoI allele, which suggests they are, in fact, part of the kindred. The coupling of the mutation to an infrequent marker also helped carrier identification in the kindred where all of 17 obligate carriers examined, including six who were not identified as carriers by enzyme assays, were found to be heterozygous for the RFLP. Thus, DNA analysis can be used for presymptomatic and prenatal diagnosis in most portions of the Nova Scotia kindred affected with Fabry disease.