of stratification according to the timing of negative life events. When categorised into early childhood and recent life events, an association between the 5-HTTLPR s allele and early-life adversities, but not recent life events, was found with depression.15, 16, 17, 18, 19, 20 Early-childhood adverse experience is proposed to exert a long-lasting impact on neurodevelopment through influencing serotonergic neurotransmission in neural circuits responsible for mood regulation. This increases the vulnerability to the negative effects of early stressors,21, 22, 23 as well as causing other possible structural and functional changes, including alterations in the programming of glucocorticoid, noradrenergic and vasopressinergic stress response systems. As a result these systems are hypothesised to show a long-lasting over-reaction to new stressors, leading to significantly impaired hippocampus and amygdala development.24, 25, 26
