Absence of association with DAT1 polymorphism and response to methylphenidate in a sample of adults with ADHD.

A polymorphism in the dopamine transporter gene (DAT1) has been previously associated with ADHD and methylphenidate has been hypothesized to block the dopamine transporter. The goal of this study was to examine whether a 40-bp variable number of tandem repeats (VNTR) of DAT1 moderate response and adverse effects associated with methylphenidate treatment of adults with ADHD. Subjects were 106 adults with ADHD enrolled in 6-week randomized placebo-controlled parallel design trials of methylphenidate (OROS and immediate release preparations). There was no evidence of an association between DAT1 VNTR and response to methylphenidate (F(2,100) = 0.04, P = 0.9). Similarly, there was no pattern of statistically significant association with DAT1 VNTR and cardiovascular or spontaneously reported adverse effects. We failed to identify an association with DAT1 and the response or tolerability of methylphenidate in adults with ADHD.