A common haplotype at the dopamine transporter gene 5' region is associated with attention-deficit/hyperactivity disorder.

The dopamine transporter (DAT) is the major site of methylphenidate action, which is one of the main drugs used to treat attention-deficit/hyperactivity disorder (ADHD). Most association studies with ADHD focused in a VNTR at the 3'-untranslated region of the gene (3'UTR) presenting 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.