Molecular genotyping of ABO blood groups in some population groups from India.

ABO blood group system is considered as one of the most important blood group systems in transfusion medicine and population genetics. The serological and genetic characteristics of this system have been well established. There are three major alleles viz., A, B and O at the ABO locus. The locus for ABO gene is on chromosome number 9 (9q 34.1 - 34.2)1. The antigenic determinants are oligosaccharides which are located on either glycospingolipids or glycoproteins. These are not direct gene products of the ABO genes. These genes encode enzymes which are collectively known as glycosyltransferases, and these enzymes transfer specific sugar residues to a precursor substance (H antigen) to produce the A and B antigens. A variety of polymorphisms has been reported in the ABO glycosyltransferase gene1. For convenience, A group glycosyltransferase sequence is considered as a reference sequence and compared to it B and O groups are identified. Initially specific restriction endonucleases were used to identify common ABO alleles2. Later on by using gene scanning techniques like denaturing gradient gel electrophoresis (DGGE), single strand conformation polymorphism (SSCP) followed by DNA sequencing, several alleles have been identified3,4. Using these techniques, several populations like Caucasians, Orientals, Amerindians, Brazilians, Kuwaitis and Jordanians5,6,7,8,9 from different countries have been screened for detection of different ABO alleles. India is a multi-ethinic country harbouring 4635 ethinic groups and 635 scheduled tribes as per the 2001 census study10. Genetic variation between inter- and intra-populations have been studied extensively in the non tribal as well as tribal populations using various blood groups and biochemical markers11,12. The ABO blood group system has been studied on the largest number of Indian populations13,14,15. In general, higher incidence of B group than A group is characteristic of the people of Indian subcontinent16,17. Knowledge of distribution of ABO blood groups is important because certain diseases and malignancies have been found to be associated with the ABO blood groups18,19,20. Bandyopadhyay et al21 studied ABO blood groups in couples with spontaneous abortions and compared them with those with normal newborns from the same area and concluded that ABO incompatibility between the couples could be responsible for early spontaneous abortions and heterozygote selection of ABO blood group genotypes. Some studies have reported the absence of significant association between malaria and ABO blood groups19, while others have shown high frequency of malaria among blood group A individuals as compared with those with other blood groups22. Carvalho et al23 have tried to find the association if any, between various ABO alleles mainly ‘O’ group alleles and falciparum malaria patients from Brazil. They could not detect significant differences in the frequency of individuals with the various alleles between malaria patients and the general population. There is no report on molecular genotyping of ABO blood groups from India. This preliminary study was carried out to assess allelic variation and the nature of diversity of ABO blood groups at molecular level in some Indian population groups.