Of the 800+ genes that have been associated with autism [16, 17], there are several related to 5-HT signaling, including the antidepressant-sensitive 5-HT transporter (serotonin transporter, SERT; 5-HTT) gene (SLC6A4) [18] and the integrin β3 gene (ITGβ3) [19], a SERT-interacting protein that influences 5-HT levels in the periphery and in the brain [20–22]. The gene discussed is ITGB3; the disease is autism.