Complement components C2, C3, and C4 (C4A and C4B) and BF polymorphisms in populations of the Indian subcontinent.

Genetic polymorphisms of the complement components (five loci: C2, C3, C4A, C4B, and BF) have been investigated in the Telugu-speaking Hindu population of Hyderabad, Andhra Pradesh, India, and the Bangali-speaking Muslim population of Dacca, Bangladesh. The available data are compared to understand the genetic variation of complement components in populations of the Indian subcontinent. The C3F and BFF alleles show wide frequency variations in different ethnic groups of India. The range of variation in the C3F allele is intermediate between European whites and southeast Asian populations, whereas the BFF allele places the Indian frequencies between European whites and African blacks. This is the first population study to investigate the C2 and C4 (C4A and C4B) polymorphisms in two distinct groups of the Indian subcontinent. For the C2 polymorphism only the C2B variant allele was observed, and its frequency was slightly higher than in European populations. In both populations the C4A and C4B loci were highly polymorphic, with a high frequency of the null alleles C4AQO and C4B*QO, which may account for the greater susceptibility to certain autoimmune diseases in populations of South Asia.