In their case-only design study of ethnically homogenous patients diagnosed with first episode depression, Bukh and partners [239] independently associated the existence of both low activity variants of the 5-HTT-linked polymorphic region in the serotonin transporter gene and the Val66Met BDNF polymorphism with the presence of stressful life events prior to onset of depression. Here, SLC6A4 is linked to major depressive disorder.