Fluorescence-assisted mismatch analysis (FAMA) for exhaustive screening of the alpha-galactosidase A gene and detection of carriers in Fabry disease

We used the fluorescence-assisted mismatch analysis (FAMA) method to screen rapidly the alpha-galactosidase A gene in patients with Fabry disease in order to identify unknown mutations and help define genotype-phenotype correlations in this X-linked lysosomal storage disorder. Chemical cleavage at mismatches on heteroduplex DNA end-labeled with strand-specific fluorescent dyes, reliably detects sequence changes in DNA fragments of up to 1.5 kb and locates them precisely. Exhaustive scanning of the a-galactosidase gene was accomplished on four polymerase chain reaction-generated amplicons, covering all seven exons, the exon-intron boundaries, and 700 bp of 5'-flanking sequence. Mutations were identified in each of the 15 patients studied from nine unrelated kindreds. Among the seven previously undescribed sequence changes, three are obviously pathogenic because they lead to premature protein termination. The other four, a splice-site mutation and three missense mutations, were the only changes found upon complete scanning of the gene and its promoter. In addition, FAMA also detects female heterozygous carriers more dependably than direct sequencing, and thus provides a valuable diagnostic test. In Fabry disease, this molecular criterion is especially important for genetic counseling since heterozygotes can be asymptomatic and their enzymatic values within the normal range.