SLC6A4 and depressive disorder: Genetic factors appear to be relevant biological determinants of treatment responses, as pedigrees with a homogenous transmission model have already been reported with similar response to the same antidepressant group in families.[4] Many recent investigations have suggested that the 5HTTLPR polymorphism has a role to play in human depression.[20] Our study also supports a relationship between serotonin transporter gene polymorphism and the efficacy of SSRIs.