An AQP1 allele associated with Co(a–b–) phenotype

The Colton (CO) blood group system consists of four antigens, Co^a, Co^b, Co3, and Co4, located on aquaporin-1 (AQP1),with Co^ahighly prevalent in all populations (99.8%). The Colton null phenotype, Co(a–b–), is very rare, and individuals with this phenotype lack the high-prevalence antigen Co3. To date, only six Co(a–b–) probands have been reported and four silencing alleles characterized. We identified an AQP1-null allele in a white woman with anti-Co3 caused by deletion of a G at nucleotide 601 (nt601delG) that results in a frameshift and premature termination (Val201Stop). Available family members were tested for the allele. Although anti-Co3 has been associated with mild to severe hemolytic disease of the fetus and newborn, the antibody was not clinically significant as evidenced by a low titer and delivery of asymptomatic newborns with moderate to weakly positive direct antiglobulin tests for all four pregnancies. Immunohematology2013;29:1–4.