AN A(EL) ALLELE-SPECIFIC NUCLEOTIDE INSERTION AT THE BLOOD-GROUP ABO LOCUS AND ITS DETECTION USING A SEQUENCE-SPECIFIC POLYMERASE CHAIN-REACTION

Genomic DNA from each of four A(el), individuals (genotypes AO(1), AO(1var), AO(2)) and one A(cl)B individual was used as a template for amplifying exons 6 and 7 of the ABO genes, which were subsequently sequenced. In all the A(el) alleles a single nucleotide insertion, compared to the A consensus sequence, was observed that would alter the amino acid sequence of the glycosyltransferase immediately after its postulated nucleotide sugar binding site and furthermore extend the translated protein by 37 amino acids (16 more than the A(2) enzyme). A sequence-specific primer PCR assay was developed to detect the nucleotide insertion. It was possible to differentiate all 20 serologically defined A(cl)/A(cl)B individuals available from 145 blood donors with normal ABO phenotypes and genotypes and 26 individuals with various A subgroups other than A(1), A(2) and A(cl). This mutation explains the A(cl) phenotype and forms the basis of a method for detecting the A(el) allele. (C) 1995 Academic Press, Inc.