Two imaging genetics studies showed that genetic variation of the DAT1 gene is associated with altered striatal volume, which may contribute to ADHD susceptibility; the caudate nucleus, a sub-region of the striatum, was found to be smaller in children homozygous for the 10-repeat allele (10/10) than in carriers of the 9-repeat allele (Durston et al. 2005; Shook et al. 2011). Here, SLC6A3 is linked to attention deficit-hyperactivity disorder.