DAR, a new RhD variant involving exons 4, 5, and 7, often in linkage with ceAR, a new Rhce variant frequently found in African Blacks

The highly polymorphic ph system is encoded by 2 homologous genes RHD and R HCE. Gene rearrangements, deletions, or point mutations may cause partial D and CE antigens. In this study, a new RHD variant, DAR, and a new RHCE var iant, ceAR, are described in 4 Dutch African Blacks. Serologically, DAR sho wed weaker reactions with a monoclonal antibody and polyclonal antiserum ag ainst D. The DAR phenotype was characterized by complete loss of at least 9 of 37 ph D epitopes. Erythrocytes expressing ceAR were all typed as VS-, V +. DNA analysis showed a partial D allele with only 3 mutations: C602G (exo n 4), T667G (exon 5), and T1025C (exon 7). The ceAR allele carried G48C (ex on 1), a hybrid exon 5 (A712G, C733G, A787G, and T800A), and A916G (exon 6) . To study the frequency of these variants, 326 South-African Blacks was sc reened genomically. Of the 326 donors, 16 (4.9%) carried the DAR allele, 20 (6.1%) the ceAR allele, and 14 (4.3%) both mutated alleles. Five of these donors (1.5%) had the DAR phenotype, indicating that they carried the DAR a llele homozygously or next to a D-negative allele. Immunogenicity of the D antigen for individuals with the DAR phenotype was proven, because 1 of the 4 Dutch individuals produced allo-antibodies against D after multiple tran sfusions with D-positive blood. In a multiethnic society, the prevalence of this D phenotype will increase and is therefore relevant in transfusion pr actice and in prevention of hemolytic disease of the newborn. (C) 1999 by T he American Society of Hematology.