Identification of the Tc^b allele of the Cromer blood group gene by PCR and RFLP analysis

The Cromer blood group antigens reside on the complement regulatory protein, decay-accelerating factor (DAF). The Cromer system comprises 10 antigens, 3 of which are of low incidence. When an individual is homozygous for the allele encoding one of these low-incidence antigens, they are liable to produce an antibody to the antithetical high-frequency antigen if challenged by pregnancy or transfusion. These antibodies are often difficult to identify, because of the lack of readily available antigen-negative cells and typing sera. In blacks, about 5 percent of individuals carry the rare Tc^b Cromer allele. We have shown that the presence of the low-incidence Tc_b allele can be detected by polymerase chain reaction (PCR) amplification of a fragment of the gene encoding DAF, followed by allelespecific restriction enzyme digestion.