Fabry disease: Twenty-two novel mutations in the alpha-galactosidase A gene and genotype/phenotype correlations in severely and mildly affected hemizygotes and heterozygotes

Background: Fabry disease, an inborn error of glycosphingolipid catabolism, results from mutations in the X-chromosomal gene encoding the lysosomal ex oglycosidase, alpha-galactosidase A (alpha-Gal A; EC 3.2.1.22). The nature of the molecular lesions in the alpha-Gal A gene in 36 unrelated families w as determined in order to provide precise heterozygote detection, prenatal diagnosis, and to define genotype/phenotype correlations. Methods: Genomic DNA was isolated from affected males and/or carrier female s from 36 unrelated families with Fabry disease. The entire alpha-Gal A cod ing region and flanking intronic sequences were analyzed hy PCR amplificati on and solid-phase or cycle sequencing. Markers closely linked to the alpha -Gal A gene were analyzed to determine if probands with the same mutations were related. Results: Twenty-two novel mutations were identified including 10 missense ( P40L, W95S, S148N, C172R, M187V, N224S, W226R, A230T, D266H, N320Y), three nonsense (Y134X, C142X, W204X in two families), three splice-site defects ( IVS2(+1), IVS3(+1), IVS4(+1)) and six small deletions or insertions (26delA in two families, 672ins37, 774delAC, 833insA, 1139delC, 1188insT). Of the remaining 12 families (33.3%), each had a previously identified mutation, e ight of which occurred at CpG dinucleotides including R112C (two families), R112H, R227Q, R227X (three families), and R301Q. Haplotype analysis of the mutant alleles that occurred in two or three presumably unrelated families revealed that the families with the rare novel alleles (W204X and 26delA) were probably related, whereas those with mutations involving CpG dinucleot ides (R112C and R227X) were not, the latter being consistent with their ori gins as independent mutational events. Genotype/phenotype correlations reve aled that certain mutations previously found in mild variant patients also were found in classic patients. In addition, the genotypes and spectrum of phenotypic severity were determined in five heterozygotes with no family hi story. Conclusions: These results illustrate the molecular heterogeneity of the le sions causing Fabry disease and emphasize the fact that CPG dinucleotides c onstitute important hot spots for mutation in the alpha-Gal A gene. These s tudies also permit precise heterozygote detection and prenatal diagnosis in these families, and delineate phenotype-genotype correlations in this dise ase.