CONFIRMATION OF ASSOCIATION BETWEEN ATTENTION-DEFICIT HYPERACTIVITY DISORDER AND A DOPAMINE TRANSPORTER POLYMORPHISM

Attention deficit hyperactivity disorder (ADHD) is a common condition of childhood the symptoms of which include inattention, excessive moto r activity, inpulsivity and distractibility. It is strongly familiar(1 ) and twin(2) and adoption studies(3,4) suggest that the familiality i s due, at least in part, to shared genes. Gillis et al(2) found concor dance rates in ADHD for MZ and DZ twins of 81% and 29% respectively. S timulant drugs leg, methylphenidate) are effective in the treatment of ADHD(5) and inhibit the dopamine transporter. This has led to the dev elopment of a hypodopaminergic hypothesis for the disease(6). Cook et al(7) examined a 3' variable number of tandem repeat (VNTR) polymorphi sm at the dopamine transporter gene (DAT1) in a sample of 49 ADHD pati ents and their parents, using the haplotype relative risk (HRR) method . They found a significant association (chi(2) = 7.29, 1 d.f., P = 0.0 07) between ADHD and the 480-bp DAT1 VNTR allele. The authors stressed the importance of independent replication and we have achieved this i n a study of 40 probands and their parents, using the same robust HRR method. As in the study of Cook ef ar we found that the 480-bp allele was preferentially transmitted to ADHD probands (chi(2) = 6.07, 1 d.f. , P = 0.014).