RHD gene polymorphisms in alloimmunized RhD-negative individuals with high rate of racial admixture

The D-negative phenotype is the result of the total RHD gene deletion in almost all Caucasians, but it accounts for only about 20% in Africans and 70% in Asians. In Africans the RHDΨ that is one of the most important causes of the D-negative phenotype. We investigated the RHD polymorphisms in D-negative phenotype mixed Brazilians who have anti-D alloantibody.

Blood samples from 130 individuals previously typed as D-negative were phenotyped again using: (a) two tube reagents (Anti-D blend reagent, Cellular line TH-28, MS-26; and Anti-D polyclonal); (b) one gel test ID-Card for Rh subgroups including C(w) and K antigen; and (c) ABO/Rh (Anti-D blend reagent, Cellular line 175-2, LDM3). The method used for RHD screening detected the presence of RHD exon 10 and intron 4. Sequence analysis was performed on PCR products amplified from genomic DNA for all 10 exons RHD gene.

We found that 118/130 (90.8%) of D-negative tested individuals had total RHD gene deletion, while 12/130 (9.2%) showed RHD gene polymorphisms. The RHDΨ was found in 10 (7.7%) individuals, one sample (0.77%) hybrid RHD-CE-D(s) /RHDΨ, and another (0.77%) weak D type 4.2.

The results showed that the RHD gene was present in 9.2% of racially mixed Brazilians who produced usually clinically significant anti-D alloantibodies. Therefore, the data showed that careful attention is necessary for clinicians in applying RhD genotyping to transfusion medicine in populations with high rate of racial admixture.