Molecular genetic analysis of the Am phenotype of the ABO blood group system

Many sequences of variants in the ABO blood group system have been analysed, but genetic information is not available on the rare Am phenotype blood group. We isolated the Am phenotype in one family and performed molecular analysis on this allele.

Exons 6 and 7 of the ABO gene were analysed using genomic DNAs from members of one family containing Am phenotype individuals via polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and DNA sequencing.

In the Am allele, two single base substitutions were detected compared with the A101 allele. Both were C --> T mutations at nucleotide positions 467 and 761. PCR-RFLP using the AccI restriction enzyme was performed to detect the Am allele in 214 samples that had already been determined as type A or O by serological tests, but no sample was found to contain an Am allele.

In this study a new allele with a single-base substitution at nucleotide position 761 was identified in the Am phenotype. We designated this new allele as A112 (according to the guidelines for human gene nomenclature) and determined that PCR-RFLP analysis using the AccI restriction enzyme will be useful for detecting this allele.