[Molecular analysis of an individual with CisAB phenotype]

To explore the molecular basis for an individual with ABO subtype.

The ABO phenotype of the proband was determined by convention serological testing. Exons 6 and 7 of the ABO gene were subjected to PCR amplification and bi-directional Sanger sequencing. Haplotypes for exons 6 and 7 of the proband was determined using an ABO haplotype-specific amplification and sequencing technique.

Red blood cells of the proband showed a 4+ agglutination strength with anti-A or anti-H, no agglutination reaction with anti-A1, and a 3+ agglutination strength with anti-B. His serum had no reaction with standard A cells, O cells or self cells, but was weakly reactive with B cells at 4℃. The proband was assigned as an ABO subtype based on his serological features. Bi-directional sequencing of the ABO gene revealed heterozygosity of 261 G/del, 297AG, 526CG, 657CT, 703GA, 803GC and 930GA, and homozygosity of 796CC in the proband. Haplotype-specific amplification and sequencing showed that one of his alleles was ABO*O.01.01, and another contained a c.796A>C variation compared with the ABO*B.01 allele, which led to replacement of methionine by leucine at position 266. Searching the ABO allele database of International Society of Blood Transfusion suggested the variation to be a novel one.

The c.796A>C variation in the ABO*B.01 allele probably underlies the CisAB subtype. Accurate identification of the ABO subtype requires combined use of serological method and genetic testing.