In 2003 a gene-environment interaction (GxE) was hypothesized to explain why life stress is a predictor for depressive episodes in some individuals, but not in others, depending on an allelic variation of the serotonin-transporter-linked promoter region (5-HTTLPR); a 2009 meta-analysis showed stressful life events were associated with depression, but found no evidence for an association with the 5-HTTLPR genotype.
Ta opazovanja so pripeljala do monoaminske hipoteze za depresijo.