English

Abstract

Polymorphisms in the genes coding for A gene leads to subgroups of A. No published data regarding the prevalence of subgroups of A blood group in Andhra Pradesh, India is available. The importance of subgrouping is that the A antigens in various subgroups may differ both quantitatively and qualitatively 1 . Some individuals with blood groups A2, A3, Ax, Ael, Aend, A2B etc., have anti-A1 antibodies and may present problems in blood grouping. At our center, the typing of A subgroup of all blood donors was done using commercial anti A1 lectin, anti-A and anti-AB antisera as per the manufacturer’s instructions. On analysis of a total of 5,505 blood groupings over a period of one year, 1,486(27%) individuals had A antigen. Of these, 1,137 (20.7%) were typed as A group and 349 (6.3%) as AB group based on the presence of associated B antigen. Of the 1,137 A group individuals,1,090(95.9%) had A1 antigen (subgroup A1) and the rest 47(4.1%) had no detectable A1 antigen (subgroup A2). Similarly among the 349 AB group individuals, 282(80.8%) had A1 antigen (subgroup A1B) and 67(19.2%) had no detectable A1 antigen (subgroup A2B). The number of individuals who lack A1 antigen is less among A group individuals in contrast to AB group individuals and this difference was found to be statistically significant (p<0.0001). This may be due to the recessive nature of A2 gene compared to A1 gene and requirement of a single A2 gene and a B gene to develop as A2B blood group phenotypically and two A2 genes or one A2 gene and one O gene to develop as A2 blood group. Some postulate the presence of a strong B gene that would suppress A1 antigen activity. 2 No other subgroups of A could be detected in the present study due to the small number of donors phenotyped for subgroups of A. Similar results were obtained in other studies from Karnataka 3 and Japan. 4 By including a much larger population, the frequency of other A subgroup antigens can also be estimated. In the present study, the prevalence of A2 and A2B sub groups was found to be 0.85 percent and 1.21% in blood donors respectively. REFERENCES 1. Thakral B, Saluja K, Bajpai M, Sharma RR, Marwaha N. Importance of weak ABO subgroups. Lab Med 2005;36:32-4. 2. Voak D, Lodge TW, Reed JV. A possible explanation for the expression of A2B phenotypes observed in some populations. Vox Sang 1970;18:471-4. 3. Shastry S, Bhat S. Imbalance in A2 and A2B phenotype frequency of ABO group in South India. Blood Transfus 2010;8:267-70. 4. Ogasawara K,Yabe R, Uchikawa M, Saitou N, Bannai M, Nakata K, et al. Different alleles cause an imbalance in A2 and A2B phenotypes of the ABO blood group. Vox Sang 1998;74:242-7. I.S. Chaitanya Kumar, A. Yashovardhan, B. Suresh Babu, Anju Verma, K.V. Sreedhar Babu, DS Jothi Bai. Department of Immuno Haematology and Blood transfsion, Sri Venkateswara Institute of Medical Sciences, Tirupati.