Association of dopamine D4 receptor (DRD4) polymorphisms with attention deficit hyperactivity disorder in Indian population

Abstract

Attention deficit hyperactivity disorder (ADHD) is a childhood onset neurobehavioral disorder. Several studies worldwide have implicated a possible association between ADHD and transmission of different polymorphisms of the dopamine D4 receptor gene (DRD4) in different ethnic groups. However, this is the first report on the transmission of different polymorphisms of DRD4 in Indian subjects. Association of 5' flanking 120-bp duplication, exon 1 12-bp duplication, and exon 3 48-bp variable numbers of tandem repeats (VNTR) were analyzed in 50 ADHD cases. Haplotype-based haplotype relative risk (HHRR) analysis and transmission disequilibrium test (TDT) were carried out to ascertain the association of these polymorphisms with the disorder. Linkage disequilibria (LD) between the polymorphisms were calculated using EH+ and 2LD programs. Our preliminary data showed lack of association between ADHD and transmission of the 5' flanking 120-bp duplication and exon 1 12-bp duplication. But, the transmissions of 6 and 7 repeat alleles of exon 3 48-bp VNTR showed significant association with ADHD. We have also examined the haplotype frequencies and biased transmission of one haplotype was observed in ADHD probands. LD analysis showed very strong disequilibrium between exon 1 12-bp duplication and exon 3 48-bp VNTR. Strong LD was also observed between the 5' flanking 120-bp duplication and exon 1 12-bp duplication. The observed association between higher repeat alleles of exon 3 48-bp VNTR and Indian ADHD children is consistent with some of the earlier reports.