A case of DNA analysis of ABO blood group variant allele A2

The ABO phenotype of a bloodstain (B) on a knife that was used as a weapon in an attempted murder case was found to be different from that of the Peruvian victim's blood (AB). Serological analysis showed that the A-antigenicity was much weaker than B antigenicity, suggesting that the victim's phenotype was A(2)B or A(3)B. So, the ABO genotypes of the knife bloodstain and the victim's blood were determined by DNA analysis. The 261st G deletion, specific to the O(1) allele, was not detected in the specimens by restriction fragment length polymorphism analysis. Also, the 871st A, specific to the A(3) allele, was not found by the allele-specific amplification method. Amplified product length polymorphism and direct sequencing methods finally demonstrated that the typical B sequence was found in one allele and a single C deletion in the 1,059th-1,061st C stretch in the other allele, indicating that the ABO phenotype of the bloodstain and victim's blood were A(2)B.