They found significant differences in norepinephrine transporter methylation levels at several cytosine-phosphate-guanine (CpG) sites between ADHD and control groups and a negative correlation between methylation of a CpG site at promoter “region 1” and norepinephrine transporter distribution in the thalamus, locus coeruleus, and the raphe nuclei (78). Here, SLC6A2 is linked to attention deficit-hyperactivity disorder.