Frequent occurrence of a variant O-1 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 O-1 allele first described in a cancer cell line is now shown to account for approximately 40% of the O alleles described to date. This variant O-1 allele has at least seven point mutations when compared to the consensus gene, in addition to the deletion characterising the normal O-1 allele.