CONTEXT: Attention-deficit/hyperactivity disorder (ADHD) is a common heritable childhood behavioral disorder. Identifying risk factors for ADHD may lead to improved intervention and prevention. The dopamine transporter gene (DAT1) is associated with ADHD in several studies, with an average 1.2 odds ratio and evidence of heterogeneity across data sets.
OBJECTIVE: To investigate sources of heterogeneity by refining the DAT1 association using additional markers and investigating gene-environment interaction between DAT1 and maternal use of alcohol and tobacco during pregnancy.
DESIGN: Prospective study.
SETTING AND PATIENTS: Children with ADHD from child behavior clinics in the southeast of England and in the Taipei area of Taiwan.
INTERVENTIONS: Within-family tests of association using 2 repeat polymorphisms in the 3' untranslated region and intron 8 plus additional markers in the English sample.
MAIN OUTCOME MEASURES: Transmission ratios of risk alleles from heterozygote parents to affected offspring and comparison of the transmission ratios in high- and low-exposure groups for the environmental variables.
RESULTS: A novel association was identified between ADHD, the intron 8 polymorphism, and a specific risk haplotype in both English and Taiwanese samples. The risk haplotype showed significant interactions with maternal use of alcohol during pregnancy.
CONCLUSIONS: The identification of a common haplotype in 2 independent populations is an important step toward identifying functionally significant regions of DAT1. Interaction between DAT1 genotypes and maternal use of alcohol during pregnancy suggests that DAT1 moderates the environmental risk and has implications for the prevention of ADHD. Further studies are required to delineate the precise causal risk factor involved in this interaction.