BACKGROUND: The Dombrock (Do) blood group system consists of six distinct antigens: Doa, Dob, Gya, Hy, Joa, and DOYA. Our finding of a pregnant patient whose red blood cells (RBCs) were Hy+ but whose serum contained an apparent alloanti-Hy suggested the presence of a seventh antigen and prompted this study.
STUDY DESIGN AND METHODS: Standard hemagglutination and polymerase chain reaction–based methods were used throughout.
RESULTS: The patient's RBCs typed as Do(a–b+w), Gy(a+w), Hy+w, Jo(a+w), and DOYA+w. Her serum agglutinated RBCs with common Dombrock phenotypes. Hy– RBC samples were very weakly reactive or nonreactive, Jo(a–) and DOYA– RBC samples were reactive, and Gy(a–) RBC samples were nonreactive. Reactivity was obtained with RBCs treated with papain or α-chymotrypsin, but not with RBCs treated with trypsin or dithiothreitol. DNA analysis showed the patient to be DO*793G (DO*B/DO*B), DO*323G, DO*350C, DO*547T, and DO*898G and revealed two homozygous nucleotide changes of DO*431C>A and DO*432C>A in Exon 2, which predicts a change of Ala (GCC) at Amino Acid 144 to Glu (GAA). This indicates that she is homozygous DO*B-WL with Nucleotide 431 and 432 changes, which without knowing the effect of the two novel changes, is predicted to encode the Do(a–b+), Gy(a+), Hy+, Jo(a+), DOYA+ phenotype.
CONCLUSIONS: The antibody in the patient's plasma recognizes the high-prevalence antigen absent from her RBCs. The Ala144Glu change caused an absence of a high-prevalence Do antigen that we have named DOMR [provisional ISBT number 014007 (DO7)]. The absence of DOMR is associated with weakening of Dob, Gya, Hy, Joa, and DOYA antigens.