SLC6A3 and Timothy syndrome: Included in our study are the dopamine receptor D2 (DRD2) and the dopamine transporter (SLC6A3/DAT1) gene that were both implicated in TS by others [3, 34, 37] and the catechol-O-methyltransferase (COMT) gene that was implicated in OCD [45], a related disorder.