Association study of vntr polymorphism in drd4 gene with intellectual disability from south india

Objective: Genetic polymorphisms associated with variation in normal intellectual ability could also cause intellectual disability (ID). Contradicting reports are available on the association of a 48-bp variable number of tandem repeat polymorphism located in exon 3 of DRD4 gene encoding dopamine receptor D4 and decreased neurocognitive functioning. This study aimed to investigate its association with idiopathic ID in a south Indian population.
Methods: DNA samples from 146 ID cases with normal karyotype and 101 healthy control individuals were amplified and visualized on agarose gel. The genotypes were determined by comparing with 50bp ladder and confirmed by sequencing of representative samples. Differences in allele and genotype frequencies were analysed using Fisher exact test.
Results: The 4R allele was found to be the most common allele in both the groups. The prevalence of the 2R allele was higher, although not significant, in ID. However, a significant protective association was observed for the 5R allele and the 4R/5R genotype (OR = 0.14; P = 0.04).
Conclusion: There was no significant association between the different repeat alleles and idiopathic ID. Extended analyses with larger sample sizes will identify rare variants carrying an increased risk for ID and also enable data comparison between various geographical regions.