Family based association analysis of statistically derived quantitative traits for drug use in ADHD and the dopamine transporter gene

Objective: To determine whether SNPs within the dopamine transporter gene (DAT) are associated with quantitative phenotypes generated from drug frequency variables in an ADHD sample. Method: 35 SNPs were genotyped in and around DAT. We developed a quantitative phenotype at each SNP by weighting the drug frequency variables. The weights were selected to maximize the heritability at each SNP. Once a quantitative phenotype was generated at each SNP, a screening procedure was used to select and test the SNPs with the greatest power to detect an association in DAT. Results: No SNPs in DAT were associated with the quantitative phenotypes generated from the drug frequency variables after the multiple comparisons adjustment; however, some SNPs achieved nominal significance. A sliding window of analysis of 3 SNPs also resulted in only nominal associations. Conclusions: SNPs in DAT do not appear to be associated with the phenotypes generated from drug frequency variables among individuals with ADHD.