A significant association of serotonin transporter polymorphism haplotypes in attention deficit hyperactivity disorder (ADHD)

Reduced central serotonergic activity has been implicated in poor impulse regulation and aggressive behaviour in animals, adults and also young children. A polymorphism in the promoter of the serotonin transporter (5HTT) has recently been implicated in ADHD. We have examined three 5HTT polymorphisms (the promoter, the VNTR in intron 2 and the 3′ UTR SNP) in a sample of 113 ADHD trios. TDT analysis of haplotypes demonstrated significant preferential transmission of haplotypes containing the T allele of the 3′UTR SNP with the long allele of the promoter polymorphism (2 = 11.96, 3df, p 0.01) and the 10 repeat of the VNTR (2 = 10.18, 4df, P <0.05). A pooled analysis of 289 cases and 372 controls from our, and other published results for the promoter polymorphism demonstrated a significant over-representation of the long allele in ADHD probands compared to controls (2 = 7.14, P <0.01). This study provides further evidence for the possible involvement of the serotonin transporter in susceptibility to ADHD.