Molecular basis of DEL phenotype in the Indian population: Insights from next-generation sequencing analysis of two cases

The DEL phenotype represents an intriguing and challenging aspect of blood group serology. This condition is characterized by an extremely weak expression of the D antigen on red blood cells, to the extent that it often eludes detection through routine serological methods. Identifying the DEL phenotype necessitates more specialized techniques, such as adsorption and elution tests, to reveal the presence of the D antigen. This distinctive phenotype underscores the complexity and subtlety of blood group genetics and highlights the importance of using advanced methods to accurately classify individuals with this condition, as their ability to form anti-D antibodies can have clinical implications during transfusion and pregnancy scenarios. There is a paucity of data for the DEL phenotype in the Indian population, and the molecular basis has not been elucidated yet. Our investigation delves into the genetic underpinnings of two distinct DEL phenotype cases that pose challenges for resolution through conventional serological techniques. We employ next-generation amplicon sequencing to unravel the intricate genetic landscape underlying these cases. In the D-negative donor, the DEL phenotype was first identified serologically, which was subsequently confirmed by molecular analysis. In the second case, it was associated with an anti-D antibody in a D-positive patient. Initial data analysis unveiled a substantial reduction in coverage across the exonic segments of the RHD gene in both samples, suggesting the potential presence of RHD exon deletions. On both occasions, we identified a homozygous intronic RHD polymorphism that is well established to be linked to the RHD* 01EL.32/RHD*DEL32 variant.