Dopamine receptor D4 exon 3 variable number of tandem repeat polymorphism: Distribution in eastern Indian population

Background: A 48bp variable number of tandem repeat (VNTR), in the dopamine receptor D4 ( DRD4 ), has been extensively studied in association with a variety of traits and neuropsychiatric disorders in different ethnic groups; the VNTR has been found to affect receptor binding.
Aims: This investigation, for the first time, compared distribution of DRD4 VNTR in different Indian populations from the eastern part of the country, belonging to Indo-Caucasoid and Indo-Mongoloid ethnicity.
Materials and Methods: 852 individuals were recruited and divided into six population groups; Brahmin, Kayastha, Scheduled Caste, Mahishya, Muslim and Manipuri (Meitei). Allele and genotype frequencies were compared among groups as well as with data available for south-western Indian population.
Results: A total of six alleles (2-7-repeats) were observed, of which the 4-repeat (4R) was most frequent. Gross genetic dissimilarities were noticed between the Indo-Caucasoid and Indo-Mongoloid ethnic groups. Muslim group lacked 5R and 7R, while Manipuri group exhibited a very high frequency of 2R. Populations from eastern India revealed lower 7R frequencies as compared to the south-western populations.
Conclusions: The DRD4 VNTR has been reported to play important role in cognition and alleles with higher repeats have been found to be associated with novelty seeking and personality traits. The present comparative analysis of different eastern Indian population would be helpful in extending our knowledge on this particular DRD4 variant. It will also be useful in understanding the behavioural differences between populations in the light of their genetic make up.

Keywords
DRD4, exon 3 variable number of tandem repeat, eastern-Indian population