Lack of association of dopamine D4 receptor gene polymorphisms with ADHD subtypes in a population sample of twins

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Abstract
Attention‐deficit hyperactivity disorder (ADHD) is a common, highly heritable syndrome of childhood characterized by problems with inattention, hyperactivity, and impulsivity. A variety of case control and family‐based transmission distortion genetic studies of ADHD have focused on the possible involvement of polymorphisms of the DRD4 receptor gene. The majority of studies have examined the association of variously defined ADHD with an exon 3 polymorphism containing a variable number of imperfect 48 base pair repeats. Recently, McCracken et al. [ 2000 : Mol Psych 5:531–536] reported an association of the DSM‐IV primarily inattentive ADHD subtype with a 5′ 120 base pair repeat polymorphism in the DRD4 gene. In this report, we test for the possible association of these two polymorphisms with population‐derived samples of DSM‐IV ADHD subtypes. Furthermore, we extend previous studies by testing for associations with ADHD subtypes derived from latent‐class analysis of interview responses. In contrast to most, but not all, previous studies, we failed to demonstrate any significant association of the exon 3 7‐repeat allele with ADHD. Nor did we replicate the association of the 5′120 base pair repeat polymorphism. We do find a significant association of the exon 3 3‐repeat allele with a novel talkative/impulsive latent‐class–defined subtype of ADHD.