Abstract
Attentionβdeficit hyperactivity disorder (ADHD) is one of the most common psychiatric disorders of childhood. The role of genetic factors in its etiology is strongly supported by family, adoption, and twin studies. Several investigations have reported associations between ADHD and both the 7βrepeat allele of the 48 bp VNTR at the DRD4 gene and the 10βrepeat allele of the 40 bp VNTR at the DAT1 gene, but the results have been inconsistent. A sample of 81 Brazilian ADHD children and adolescents and their parents were screened for these DRD4 and DAT1 VNTRs. An excess of the DRD4 7βrepeat allele was observed when both ADHD probands and their parents were compared with an ethnically matched control sample (chiβsquareβ=β11.55, Pβ=β0.03; chiβsquareβ=β12.17, Pβ=β0.03, respectively). However, haplotype relative risk (HRR) analysis showed no preferential transmission of the DRD4 7βrepeat allele. No evidence of association with the DAT1 polymorphism was detected by both approaches. Nevertheless, an interaction effect of both genes on ADHD hyperactive/impulsive dimension was observed (Fβ=β4.68; Pβ=β0.03). These results add to the group of studies that together suggest a small effect of these genes in the susceptibility to ADHD. Β© 2001 WileyβLiss, Inc.