Fabry disease: identification of novel alpha-galactosidase A mutations and molecular carrier detection by use of fluorescent chemical cleavage of mismatches.
Fabry disease (FD) (angiokeratoma corporis diffusum) is an X-linked inborn error of glycosphingolipid metabolism caused by defects in the lysosomal alpha-galactosidase A gene (GLA). The enzymatic defect leads to the systemic accumulation of neutral glycosphingolipids with terminal alpha-galactosyl moieties. Clinically, affected hemizygous males have angiokeratoma, severe acroparesthesia, renal failure, and vasculopathy of the heart and brain. While demonstration of alpha-galactosidase deficiency in leukocytes is diagnostic in affected males, enzymatic detection of female carriers is often inconclusive, due to random X-chromosomal inactivation, underlining the need of molecular investigations for accurate genetic counseling. By use of chemical cleavage of mismatches adapted to fluorescence-based detection systems, we have characterized the mutations underlying alpha-Gal A deficiency in 16 individuals from six unrelated families with FD. The mutational spectrum included five missense mutations (C202W, C223G, N224D, R301Q, and Q327K) and one splice-site mutation [IVS3 G(-1) --> C]. Studies at the mRNA level showed that the latter led to altered pre-mRNA splicing with consequent alteration of the mRNA translational reading frame and generation of a premature termination codon of translation. By use of this strategy, carrier status was accurately assessed in all seven at-risk females tested, whereas enzymatic dosages failed to diagnose or exclude heterozygosity.