SLC6A9 and attention deficit-hyperactivity disorder: In addition, we evaluated other candidate genes frequently reported as being related with ADHD such as STS, FADS2 and SNAP25. Finally, significantly reported genes from GWAS studies such as CDH13, GFOD1, SLC6A9 and GRM7, and genes revealed in linkage as playing a role in ADHD susceptibility such as LPHN3 were included in the study (Table 1).