Genetics of apolipoprotein H (β2-glycoprotein I) polymorphism in India

Background: Human apolipoprotein H (beta(2)-glycoprotein I, apoH, protein; APOH, gene) is a single-chain glycoprotein that has been implicated in several metabolic pathways, including lipid metabolism, coagulation and production of antiphospholipid antibodies and many disease phenotypes. The structural, molecular and genetic bases of APOH have been studied in detail but population studies, especially from the Indian subcontinent, are limited. Objective: This study seeks to enlarge our understanding of APOH genetic diversity in human populations from different regions and social groups of India. Also, we examine the level and extent of genetic variation at this locus in world populations and its utility as a population genetic marker. Subjects and methods: Blood samples from 1381 unrelated and randomly selected individuals were screened for APOH genetic polymorphism. Eleven populations from North India (Brahmins, Banias, Jat Sikhs, Khatris, Scheduled Castes, Lobanas and Rajputs), West India (Brahmin and Patels) and Central India (Brahmins and Baiga tribe) were studied for APOH polymorphism using isoelectric focusing. Allele frequencies were calculated by the gene counting method. The results were statistically evaluated using chi-square statistics for regional and ethnic variation. Genetic distances were computed on Indian populations to determine the population affinities. Correspondence analysis was used to assess ethnic variation in world populations. Results: An interesting and wide genetic variation at this locus was observed in Indian populations. The frequency distribution of three observed alleles ranged from 0.034 to 0.091 for APOH* 1, 0.852 to 0.917 for APOH* 2 and 0.027 to 0.075 for APOH*3. The world's highest APOH* 2 allele frequency was observed in the Patel (0.917) caste group from West India. Conclusions: Overall, the observed variation at this locus in Indian populations is comparable to many Caucasian populations. An analysis of world populations showed that APOH is a useful genetic marker for population and anthropological studies.