Haplotype diversity and linkage disequilibrium at the DRD2 locus among the tribes of western and southern regions of India

Background: Dopamine receptor D2 (DRD2) is an important gene having functional significance in the fields of neuropsychiatry and pharmacology and also has importance in evolutionary studies.
Materials and Methods: This study was undertaken to find out the haplotype distribution and linkage disequilibrium (LD) pattern for the three TaqI sites (TaqI ′A′, TaqI ′B′ and TaqI ′D′) in the DRD2 gene in 232 unrelated individuals from five ethno-linguistically distinct endogamous tribal populations; Siddis and Gonds of Uttara Kannada district, Karnataka; Varli and Kolgha of Valsad district, Gujarat; and Dangi Konkana of Dang district, Gujarat. The genotype data obtained after molecular analysis of the three DRD2 sites was subjected to statistical analysis such as calculation of allele frequencies, haplotype frequencies among others. Subsequently, a neighbor-joining tree was also constructed from the data obtained.
Results: The three DRD2 sites were found to be polymorphic in all the populations. All the populations showed high levels of heterozygosities. Out of the eight possible haplotypes, most populations shared seven haplotypes. Of all the populations, Siddis showed the highest frequency of the ancestral haplotype B2D2A1 (11.4%). Significant LD was found to exist for TaqI ′A′ and TaqI ′B′ sites in both the populations.
Conclusion: The findings are in concurrence with those from other Indian studies, especially from Dravidian-speaking South Indian populations. Similar pattern of diversity observed for ethnically and linguistically diverse populations in the present study is indicative of complex structure of Indian populations.

Keywords
Ancestral haplotype, ethno-linguistic diversity, haplotype analysis, linkage disequilibrium, population structure