A second more recent body of research has focused on whether the effects of 5-HTTLPR on psychiatric disorders are moderated by exposure to stressors. A widely-cited study found no direct association between 5-HTTLPR and depression, yet revealed that, among those exposed to major life stressors, the short allele was related to depressive symptoms in an additive fashion: levels of depressive symptoms were lowest among persons with L/L genotype, intermediate among S/L, and highest among those with S/S genotype [8]. They found a similar pattern among adults exposed to child maltreatment. Subsequent attempts to replicate these findings yielded mixed results. Two recent meta-analyses concluded that there is no evidence of such a gene-environment (GxE) interaction [9, 10], but most of the studies evaluated focused on major life stressors rather than more severe trauma.
