Finally, a double-blind, 6-week, placebo-controlled trial by Mick et al. [35] had the objective of investigating whether dopamine transporter (DAT1) genetic variants (10-bp variable number of tandem repeats (VNTR) in the 3′-untranslated region (UTR), i.e., homozygous for the 10-repeat DAT1 allele versus heterozygous 9/10 or homozygous 9-repeat) might modulate the effectiveness of MPH in 285 adults with ADHD. Here, SLC6A3 is linked to attention deficit-hyperactivity disorder.