SLC6A3 and attention deficit-hyperactivity disorder: Specifically, the relationship between VNTR polymorphism of DAT1/SLC6A3 gene and ADHD, as well as the relationship between this polymorphism and alcoholism, have been previously studied (reviews: [3, 38, 39]) and, furthermore, meta-analysis of the influence of VNTR polymorphism of DAT1/SLC6A3 gene on ADHD indicated a statistically significant relationship (OR = 1.12, 95 % CI: 1.00-1.27) [40].