HLA DRB1* and DQB1* allelic diversity among Nadars: a primitive south Indian Dravidian caste group

South India is one of the oldest geophysical regions occupied mainly by Dravidian language-speaking people. In the present study, 84 unrelated healthy Nadar individuals from Tamil Nadu State were analyzed for human leukocyte antigen (HLA) DRB1* and DQB1* allele frequencies and their haplotype frequencies were analyzed by high resolution polymerase chain reaction (PCR)-typing of genomic DNA. Results revealed that Nadars possessed >0.1 allele frequencies of HLA DRB1*15011, 03, 04, 1404, 0701, 1001, and DQB1*0201, 03, 0501, and 0503. The highest frequencies of DRB1*0317 (0.048), DRB1*1317 (0.012), and DRB1*1404 (0.107) in the world were found among the Nadar caste. The most frequent two-locus haplotypes identified among the Nadars were DRB1*0701-DQB1*0201 and DRB1*1000-DQB1*0501, and DRB1*1404-DQB1*0503 and DRB1*15011-DQB1*0601. When compared with world populations, HLA DRB1*1322, DRB1*1434, and DQB1*0614 were identified exclusively among Nadars. The heterozygosity and Watterson's homozygosity tests indicated that balancing selection still operates among the South Indian caste groups. The hierarchical cluster analysis for DRB1 data from the Indian caste and population groups showed that the Nadars cluster with Kashmir Brahmins and North Indians. The present study shows that the Nadar caste has several unique alleles and haplotypes at high frequency that are rare or absent in other populations of India and the world.