Molecular basis of weak D expression in the Indian population and report of a novel, predominant variant RHD allele.

Background: The Rh blood group system is the most polymorphic system and is implicated in hemolytic transfusion reaction and hemolytic disease of the fetus and newborn. Molecular genetics of the RH genes have been extensively studied in Caucasians, Africans, and East Asians and the variant alleles giving rise to weak and partial D phenotypes have been reported. However, limited genetic studies have been carried out in the large Indian population, even though the variability of Rh expression has been documented.

Study Design And Methods: In this study we sought to characterize the molecular bases of weak D expression in Indians. RHD gene in samples presenting with a weak D phenotype by serologic analyses (n = 223) was genotyped by conventional molecular approaches.

Results: In addition to referenced and novel single-nucleotide variations, a novel approximately 12-kb duplication event, including Exon 3, was identified predominantly in variant D samples (130/223, 58.3%) and characterized at the nucleotide sequence level. Functional analyses suggested that this genetic variation quantitatively affects the expression of the normal transcript and then subsequently the expression of the normal RhD protein.

Conclusion: We describe a major novel, variant RHD allele in Indians that can be easily identified routinely by implementing a simple genotyping assay. Although we may consider this variation as a weak partial D variant, further studies and observations are needed to confirm the same. These findings may contribute to improve significantly Rh blood group diagnostics in more than one billion Indians.