ASD: autism spectrum disorders, SSRIs: selective serotonin reuptake inhibitors, SNRIs: serotonin-norepinephrine reuptake inhibitors, TCAs tricyclic antidepressants, DAT: dopamine transporters, NET: norepinephrine transporters, ADHD: attention deficit and hyperactivity disorder, KCC2: K-Cl co-transporter, NMDA: N-methyl-D-aspartate. This evidence concerns the gene SLC6A3 and attention deficit-hyperactivity disorder.