The serotonin transporter gene (SERT, 5-HTT), coding for a solute carrier family 6 member 4 protein (SLC6A4) was reported to carry both common and rare variants as well as a high-expressing haplotype associated with increased gene expression (5-HTTLPR/rs25531/rs25532) and protein activity (p.I425V), thus potentially contributing to serotonergic abnormalities in TS with or even more so, without OCD (Kilic et al., 2003; Moya et al., 2013). This evidence concerns the gene SLC6A4 and Timothy syndrome.