Attention deficit hyperactivity disorder: Association with the dopamine transporter (DAT1) but not with the dopamine D4 receptor (DRD4)

Attention deficit hyperactivity disorder (ADHD) is a common condition of childhood. It is strongly familial and is thought to be due, at least in part, to shared genes. The dopamine transporter (DAT1) and the dopamine D4 receptor (DRD4) genes have been implicated in the etiology of this disorder. Cook et al. examined a 3′ variable number of tandem repeats (VNTR) polymorphism at DAT1 in a sample of 49 ADHD patients and their patients, using the haplotype relative risk (HRR) method. They found a significant association (χ² = 7.29, 1 d.f, P = 0.007) between ADHD and the 480-bp DAT1 VNTR allele. In a sample of 40 probands and their parents and using the same study design, we have confirmed the above association. In order to reconfirm this association within the Irish population, we examined a new set of probands and their parents. We found a strong trend of association, although not significant, with the 480-bp DAT1 VNTR allele (χ² = 3.32, 1 d.f, P - 0.068). However, our combined samples demonstrated a very strong association (χ² = 8.35, 1 d.f, P = 0.0038). We also examined the 48-bp repeat sequence of DRD4 in a sample of 69 probands and their parents. Contrary to previous findings, we did not confirm an association between D4.7 allele and ADHD.