While investigating the effect of three SLC6A3 alleles (10/10 genotype, and the haplotypes 10–6 and 9–6) on striatum volume in ADHD patients, another volumetric-based study reported that carriers of the SLC6A3 haplotype 9–6 had around 6% bigger striatum volume than non-carriers130. Here, SLC6A3 is linked to attention deficit-hyperactivity disorder.