Attention-deficit hyperactivity disorder: A study of association with boththe dopamine transporter gene and the dopamine D4 receptor gene

Attention-deficit hyperactivity disorder (ADHD) is one of the most common p sychiatric disorders of childhood. The role of genetic factors in its etiol ogy is strongly supported by family, adoption, and twin studies, Several in vestigations have reported associations between ADHD and both the 7-repeat allele of the 48 bp VNTR at the DRD4 gene and the 10-repeat allele of the 4 0 bp VNTR at the DAT1 gene, but the results have been inconsistent. A sampl e of 81 Brazilian ADHD children and adolescents and their parents were scre ened for these DRD4 and DAT1 VNTRs, An. excess of the DRD4 7-repeat allele was observed when both ADHD probands and their parents were compared with a n ethnically matched control sample (chi-square = 11.55, P = 0.03; chi-squa re=12.17, P=0.03, respectively), However, haplotype relative risk (HRR) ana lysis showed no preferential transmission of the DRD4 7-repeat allele, No e vidence of association with the DAT1 polymorphism was detected by both appr oaches, Nevertheless, an interaction effect of both genes on ADHD hyperacti ve/impulsive dimension was observed (F = 4.68; P = 0.03), These results add to the group of studies that together suggest a small effect of these gene s in the susceptibility to ADHD. (C) 2001 Wiley-Liss, Inc.