Molecular characterization of variant D antigen expression among 56,445 blood donors in East India

Transfusion of red cells from RhD-positive donors to recipients lacking all or some epitopes of the D antigen can lead to the development of anti-D, potentially resulting in hemolytic transfusion reactions. Over 500 RHD alleles affect the qualitative or quantitative expression of the D antigen. There are huge differences in their prevalence among populations. Despite the distinct genetic diversity across multiple sub-populations in India, the prevalence of RHD alleles in the East Indian region has remained unknown.

Standard hemagglutination tests were performed, along with molecular techniques to determine the nucleotide sequence of the RHD gene.

Over 3 years, 56,445 blood donors were tested at the Tata Medical Center, Kolkata by serology. We found 23 samples with D-discrepant test results in immediate spin anti-D technique (0.04%), all of them were C+c+. Variant RHD alleles were identified in 15 samples (15/23, 65.2%). The Indian-type weak D (RHD*01W.150) was the most common variant (30.4%, No.=7), occurring in 1 in 8,063 blood donors in East India versus 1 in 729 blood donors in South India (p<0.001). Other identified variants included RHD*06.03.01 (No.=3), RHD*17.05 (No.=2), RHD*01.EL.37 (No.=2), and RHD*01W.96 (No.=1). The remaining 8 samples (8/23, 34.8%) carried the reference RHD allele (RHD*01.01).

Our findings reveal a lower prevalence of Indian-type weak D in East India than South India, indicating region-specific genetic diversity. The high incidence of wild-type RHD allele with D-discrepancy in East India suggests a potentially novel molecular mechanism. While RHD*06.03.01 and RHD*17.05 have, the 3 others identified RHD alleles have not been associated with anti-D alloimmunization. We recommend D-negative transfusion for individuals with D-variants that have documented alloimmunization, and advocate to investigate the clinical significance of other D-variant alleles prevalent in East India, such as the Indian-type weak D.