New antigen in the Dombrock blood group system, DOYA, ablates expression of Do(a) and weakens expression of Hy, Jo(a), and Gy(a) antigens.

BACKGROUND: The Dombrock (Do) blood group system consists of five distinct antigens: Do(a), Do(b), Gy(a), Hy, and Jo(a). Our finding of a patient whose plasma contained a Do-related alloantibody suggested the presence of a sixth antigen.

STUDY DESIGN AND METHODS: Standard hemagglutination, flow cytometry, and polymerase chain reaction (PCR)-based methods were used throughout. Protein homology modeling was used to map the amino acid change on the protein structure.

RESULTS: The patient's red blood cells (RBCs) typed as Do(a-b-), Hy+(w), Jo(a+(w)), and Gy(a+(w)). The patient's plasma agglutinated RBCs with common Dombrock phenotypes. Reactivity with Hy- and Jo(a-) RBC samples was weak, and Gy(a-) RBC samples were nonreactive. DNA analysis showed the patient to be DO*793A (DO*A/DO*A), DO*323G, and DO*350C, which predicts the Do(a+b-), Hy+, and Jo(a+) phenotype, and revealed a homozygous single-nucleotide change of 547T>G in Exon 2 that is predicted to change tyrosine at Amino Acid Position 183 to aspartic acid. This missense substitution introduced a BtgZI restriction enzyme site. The sequence data were confirmed with a PCR-restriction fragment length polymorphism assay and revealed that the patient's parents and children were heterozygous DO*547T/G. Homology modeling predicted that the 183Tyr substitution by Asp altered the Cys182 environment and influenced the formation and/or stability of the Cys182-Cys231 disulfide bond.

CONCLUSION: The patient's DO genes have a single-nucleotide change, which leads to the absence of the high-prevalence antigen DOYA. The absence of this antigen is associated with 183Asp and silencing of Do(a) and weakening of Gy(a), Hy, and Jo(a) antigens.