High frequency of partial DIIIa and DAR alleles found in sickle cell disease patients suggests increased risk of alloimmunization to RhD.

We have set out to determine the frequency of DIIIa and DAR alleles among sickle cell disease (SCD) patients. These D variants permit the unexpected development of antibodies to RhD among individuals who are otherwise classified as RhD+. DNA samples from 130 SCD patients were tested for 455A>C (specific for DIIIa), 602C>G, 667T>G (common for both DIIIa and DAR) and 1025T>C (specific for DAR) by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and sequence analysis. The PCR-RFLP showed that 12 (9.2%) of the SCD patients were carrying DIIIa and DAR alleles. Genomic DNA analysis performed by sequence showed that three samples were heterozygous DIIIa (2.3%), seven heterozygous DAR (4.6%) and two (1.5%) samples carried a partial D with four mutations: 455A>C (heterozygous), 602C>G and 667T>G (homozygous) and 1025T>C (heterozygous), indicating compound heterozygosity for one DIIIa allele and one DAR allele. The predicted phenotypes of eight (6.2%) SCD patients were DIIIa, DAR and DIIIa/DAR. Three patients were anti-D immunized (DAR, n = 1; DIIIa/DAR, n = 2). These findings suggest that SCD patients who are candidates for chronic transfusion may benefit from genotyping for DIIIa and DAR to prevent alloimmunization.