The serotonin transporter gene (SLC6A4) has been studied extensively in eating disorders (ED) using association methodologies. In particular, analysis of a common 5-HTTLPR functional polymorphism has not shown definitive conclusions. Interestingly, rare coding variants have been identified in SLC6A4 gene that could contribute to understand the role of this gene in ED. A gain-of-function variant (Gly56Ala, rs6355) was identified in a large reference sample () and associated with autism in females carriers of Ala56 allele (). In addition, functional studies of Gly56Ala polymorphism reported that Ala56 allele demonstrated elevated serotonin re-uptake transport activity compared with Gly56 transfected cells. Also, both variants showed insensitivity to activators of protein kinase G (PKG) and p-38 mitogen-activated protein kinase (MAPK) and phosphorylation studies showed elevated basal levels after 8BrcGMP stimulation treatment (, ).