Serological Characteristics and Gene Sequencing of Rare A1.02/BA.04 Blood Type

The typical serological profile of the B(A) subgroup is characterized by ABweak, with the primary genetic combination being heterozygosity between the B(A) allele and the O allele. When the B(A) allele is heterozygous with A allele, it is theoretically predicted to manifest as a normal AB phenotype. However, our study identified the presence of the B(A) allele in sample exhibiting an ABweak serological phenotype, challenging the conventional genotype-phenotype correlation.

After obtaining blood samples from our case (a 41-year-old pregnant woman), we amplified, direct-sequenced, and analyzed ABO blood groups on microcolumn glass beads (results were verified with the saline tube method). Haplotype sequencing was also performed to determine possible heterozygous genes.

Blood-group serological results revealed that the blood type was subgroup ABweak. Direct sequencing and haplotype sequencing revealed that one allele had a c.467C>T type A1.02 mutation, while the other allele had c.297A>G, c.526C>G, c.640A>G, c.657C>T, c.703G>A, c.796C>A, c.803G>C, and c.930G>A type BA.04 mutations. The specimen genotype was ABO*A1.02/BA.04.

When BA.04 and A1.02 alleles were present together, the blood type serology of the B(A) subgroup was atypical. Hence, we concluded that using only blood type serology to predict ABO subgroup is unreliable. Gene sequencing is required for accuracy.