Heterogeneity of O blood group in India: Peeping through the window of molecular biology

Molecular genotyping of ABO blood group system has identified more than 60 "O" group alleles based on the single-nucleotide polymorphisms present in the ABO gene. Heterogeneity of O group alleles has been observed in various countries from South America, Europe, Middle East, and Asia. India is a vast country with more than 1300 million population which is divided into various ethnic and tribal groups. However, very little is known about the heterogeneity of O alleles in Indians.

A total of 116 O group individuals from the mixed population of Mumbai, India, were enrolled in the present study. DNA was extracted using the standard phenol-chloroform method. The exons 6 and 7 of the ABO gene were genotyped by polymerase chain reaction-single-strand conformation polymorphism and/or DNA sequencing. The genotyping results were compared with our earlier findings.

Overall, ten different genotypes were identified. Three rare alleles, namely, O05, O11, and O26 were seen in the mixed group category. These results suggest that there is an internal heterogeneity in the mixed group while Dhodias and Parsis, the groups which were screened earlier, seem to be more homogenous groups. An important piece of information emerges out from this study, that is, O01O02 genotype is expressing some selective force in population groups screened in India as well as many other groups worldwide.

In the future, molecular genotyping of the ABO blood group system among different ethnic and tribal Indian groups would help in generating data to fill up the gaps in the molecular ABO map of the world.