The evidence described above provides us with new insight into how the most common alleles of the human DAT1 genotype (the 40 bp variable number of tandem repeats, VNTR, in the 3′ UTR of the DAT1 gene) affect methylation dynamics at the 5′ UTR of the DAT1 gene, an epigenetic modification associated with ADHD [10,14]. This evidence concerns the gene SLC6A3 and attention deficit-hyperactivity disorder.