OBJECTIVETo study the molecular genetic background of B subtype in Chinese Han population and identify novel allele at the ABO locus.

METHODSTen samples from randomly selected blood donors of normal B phenotype used as control, and six samples from individuals diagnosed as B subgroup by serological tests were genotyped by sequence specific primer polymerase chain reaction and direct DNA sequencing at the exons 6 and 7 of ABO gene. The exons 6 and 7 and the intervening intron 6 of the B allele from each B subgroup sample were analyzed by cloning and haplotype sequencing.

RESULTSA novel B variant allele was identified in two individuals whose blood samples were diagnosed as belonging to Bx subgroup and Bw subgroup respectively, the novel B allele being different from the allele B101 by single 695T>C missense mutation in exon 7. A family with the individual possessed Bx subgroup was studied. Among 22 family members tested, seven family members were found to carry the novel B variant allele. No novel point mutation at the exons 6 and 7 of ABO gene were detected in the ten control samples and the other four samples with B subgroup.

CONCLUSIONThe present authors define this allele as a novel B variant allele. The mutation of this novel allele, in which the nucleotide alters from T to C at position of 695 in exon 7 and hence results in an amino acid change from Leu to Pro, is expected to diminish the enzyme's activity. It indicates that the alteration of amino acid at the position of 232 is critical to the activity of glycosyltransferases.