Frequent occurrence of a variant O1 gene at the blood group ABO locus

Blood group ABO polymorphism was analysed in genomic DNA isolated from 150 blood donors by restriction endonuclease digestion of three polymerase chain reaction-amplified exons in the ABO genes and by sequencing of randomly selected samples. An anomalous O1 allele first described in a cancer cell line is now shown to account for approximately 40% of the O alleles described to date. This is 10 times more frequent than the only other known variant O allele (O2). This variant O1 allele has at least seven point mutations when compared to the consensus gene, in addition to the deletion characterising the normal O1 allele.