Objective: The dopamine transporter (DAT1) gene has been implicated in attention-deficit/hyperactivity disorder (ADHD), although the mechanism by which it exerts its effects remains unknown. The polymorphism associated with ADHD has been shown to affect expression of the transporter in vitro and in vivo. Dopamine transporters are predominantly expressed in the striatum, but also in the cerebellar vermis. Stimulant medication is often effective in ADHD and is believed to exert its effects by blocking dopamine transporters in the striatum. We set out to investigate the effect of the DAT1 genotype in ADHD in a small, preliminary study. We hypothesized that the DAT1 genotype would affect brain activation patterns in a manner similar to that of stimulant medication, with the lesser expressing allele mirroring its effects.
Method: We investigated DAT1 gene effects on brain activation patterns in an all-male sample of sibling pairs discordant for ADHD (n = 20) and controls (n = 9). All of the subjects participated in a functional magnetic resonance imaging session using a go/no-go paradigm and provided a DNA sample for analysis.
Results: DAT1 genotype affected activation in the striatum and cerebellar vermis. The genotype interacted with familial risk of ADHD in the striatum but not the vermis.
Conclusions: These preliminary results suggest that the DAT1 gene effects in the striatum are involved in translating the genetic risk of ADHD into a neurobiological substrate. As such, this study represents a first step in elucidating the neurobiological mechanisms underlying genetic influences in ADHD. Furthermore, these results may contribute to long-term possibilities for the development of new treatments: If the DAT1 genotype has differential effects on striatal activation, then it may be useful as a surrogate endpoint in individualized treatments targeting genotype/functional magnetic resonance imaging activation profiles.
Trial registration: ClinicalTrials.gov NCT00143832.