Attention deficit/hyperactivity disorder children with a 7-repeat allele of the dopamine receptor D4 gene have extreme behavior but normal performance on critical neuropsychological tests of attention

An association of the dopamine receptor D4 (DRD4) gene located on chromosom e 11p15.5 and attention deficit/hyperactivity disorder (ADHD) has been demo nstrated and replicated by multiple investigators. A specific allele [the 7 -repeat of a 48-bp variable number of tandem repeats (VNTR) in exon 3] has been proposed as an etiological factor in attentional deficits manifested i n some children diagnosed with this disorder. In the current study, we eval uated ADHD subgroups defined by the presence or absence of the 7-repeat all ele of the DRD4 gene, using neuropsychological tests with reaction time mea sures designed to probe attentional networks with neuroanatomical foci in D 4-rich brain regions. Despite the same severity of symptoms on parent and t eacher ratings for the ADHD subgroups, the average reaction times of the 7- present subgroup showed normal speed and variability of response whereas th e average reaction times of the 7-absent subgroup showed the expected abnor malities (slow and variable responses). This was opposite the primary predi ction of the study. The 7-present subgroup seemed to be free of some of the neuropsychological abnormalities thought to characterize ADHD.