Correlation of a missense mutation in the human Secretor alpha 1,2-fucosyltransferase gene with the Lewis(a+b+) phenotype: a potential molecular basis for the weak Secretor allele (Sew).

A missense mutation (A385 to T), predicting an Ile129 to Phe substitution, in the human Secretor alpha 1,2-fucosyltransferase gene was present in double dose in Lewis(a+b+) individuals, but not in Lewis(a-b+) individuals. Co-segregation of the Lewis(a+b+) phenotype with homozygosity for the mutation was also verified. These results yield a potential molecular basis for the weak Secretor allele (Sew) accounting for the Lewis(a+b+) phenotype.