American Journal of Medical Genetics Part B (Neuropsychiatric Genetics) 147B:1568–1575 (2008) A Common Haplotype at the Dopamine Transporter Gene 5 0 Region is Associated With Attention-Deficit/Hyperactivity Disorder Ju ´ lia P. Genro, 1 Guilherme V. Polanczyk, 2 Cristian Zeni, 2 Ange ´ lica S. Oliveira, 1 Tatiana Roman, 1 Luis A. Rohde, 2 and Mara H. Hutz 1 * 1 Departamento de Gene´tica, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil 2 Departamento de Psiquiatria, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil The dopamine transporter (DAT) is the major site of methylphenidate action, which is one of the main drugs used to treat attention-deficit/hyper- activity disorder (ADHD). Most association studies with ADHD focused in a VNTR at the 3 0 -untranslated region of the gene (3 0 UTR) pre- senting conflicting results. However, the most common explanation to inconsistent results is variable linkage disequilibrium with an adjacent functional variant, just a few number of DAT1 studies have reported LD structure across the gene. In this study, we screened 16 polymorphisms across the DAT1 gene to understand LD structure in a Brazilian sample of families with ADHD probands and to verify if there were evidence for a biased transmission of alleles and haplotypes from parents to their 243 children with ADHD. In the DSM-IV combined subtype, we observed a preferential transmission of the haplotype A/C/C/ C/A derived from five SNPs (rs2550948, rs11564750, rs261759, rs2652511, rs2975223) in 5 0 region (P corrected ¼ 0.018) and no association with any allele/haplotype at the 3 0 region of the gene, including the 3 0 VNTR and the VNTR of intron 8. These results suggest a role for the promoter region in ADHD susceptibility and that allele heterogeneity should be highly considered in DAT1 gene association studies highlighting the importance of this gene in the genetics of the disorder. ß 2008 Wiley-Liss, Inc. KEY WORDS: DAT1; SLC6A3; promoter region; linkage disequilibrium Please cite this article as follows: Genro JP, Polanczyk GV, Zeni C, Oliveira AS, Roman T, Rohde LA, Hutz MH. 2008. A Common Haplotype at the Dopamine Transpor- ter Gene 5 0 Region is Associated With Attention-Deficit/ Hyperactivity Disorder. Am J Med Genet Part B 147B: 1568–1575 INTRODUCTION Attention-deficit/hyperactivity disorder (ADHD) is one of the most prevalent mental health disorders in childhood and adolescence, affecting 5.3% of children worldwide [Polanczyk et al., 2007]. ADHD is a very heterogeneous disorder characterized by symptoms of inattention, hyperactivity and impulsivity determining significant impairment across the life cycle. Although its etiology remains unclear, there is strong evidence supporting the role of genes in the disorder [Faraone et al., 2005]. Multiple lines of evidence suggest dopamine (DA) system dysfunction in the pathogenesis of ADHD [DiMaio et al., 2003]. The dopamine transporter (DAT) is a plasma membrane protein that controls dopaminergic neurotransmission by reuptake of released dopamine into presynaptic neurons. DAT is also the main target for methylphenidate (MPH), the most used stimulant for ADHD treatment. MPH blocks the action of DAT, increasing synaptic dopamine concentrations [Bannon, 2005]. In animal studies, DAT knock-out mice presents a significant increase in motor activity with deficits in learning, memory and social interactions, representing a good animal model for ADHD [Giros et al., 1996; Rodriguiz et al., 2004]. Altogether, these data make the dopamine transporter locus (DAT1 or SLC6A3) a primary candidate gene to examine in ADHD. The DAT1 gene is mapped on chromosome 5p15.3 [Vanden- bergh et al., 1992] and consists of 15 exons separated by 14 introns that span more than 52 kb. The protein-coding portion begins within exon 2 and ends near the beginning of exon 15. This coding sequence presents strong conservation, suggesting that individual differences in DAT expression must arise from regulatory sequences [Bannon et al., 2001]. Recently, several linkage studies have been reported for ADHD. Although there is some overlap in significant linkage peaks, the most consistent is with the distal region of chromosome 5, which was reported in four independent studies [Bakker et al., 2003; Arcos-Burgos et al., 2004; Ogdie et al., 2004; Hebebrand et al., 2006], but not replicated by others [Asherson et al., 2008; Faraone et al., 2008; Romanos et al., 2008]. Ogdie et al. [2006] performed a pooled affected sib pairs (ASP) analysis with two of these previous studies [Bakker et al., 2003; Ogdie et al., 2004], suggesting a common risk locus at 5p13 and genetic heterogeneity between the two studies. These authors proposed that interpopulation variability in linkage signals might reflect differences in underlying sus- ceptibility alleles for ADHD. Because the DAT1 gene is located at the distal end of 5p, it is the most obvious candidate to explain the linkage signal in this region. Mick and Faraone [2008] recently suggested that the lack of replication across linkage studies support the idea that genes with large effects are not related to the etiology of the disorder. Because linkage studies have low power to detect linkage to *Correspondence to: Mara H. Hutz, Ph.D., Departamento de Gene ´tica, Instituto de Biocie ˆncias, UFRGS, Caixa Postal 15053, 91501-970 Porto Alegre, RS, Brazil. E-mail: mara.hutz@ufrgs.br Received 18 June 2008; Accepted 25 August 2008 DOI 10.1002/ajmg.b.30863 Published online 18 September 2008 in Wiley InterScience (www.interscience.wiley.com) ß 2008 Wiley-Liss, Inc.