[Molecular genetic analysis of an Ax13B phenotype of ABO subtype]

To explore the molecular basis for a rare Ax13B phenotype of the ABO subtype.

Serological assays were carried out to characterize the erythrocyte phenotype of the discrepant sample. Exons 6 and 7 of the ABO gene were amplified with polymerase chain reaction and subjected to direct sequencing. The amplicons were also cloned to separate the two alleles.

Both A and B antigens were detected on the red blood cells of the proband, and anti-A antibody was detected in the serum. The serological phenotype of the sample was identified as AxB. DNA sequencing showed heterozygous status for 297AG, 526CG, 657CT, 703AG, 796AC, 803GC, 930GA and 940AG in exons 6 and 7. After cloning and sequencing, two alleles Ax13 and B101 were obtained. The sequence of Ax13 showed a nucleotide change (A to G) at position 940.

The 940A>G mutation of the α-1,3-N-acetylgalactosaminyltransferase gene has resulted in the reduced expression of A antigen.