In girls carrying the low activity allele of MAOA, the level of depression in carriers of 5-HTTLPR S-allele increased significantly after stressful life events, while the interaction between 5-HTTLPR L-allele and stressful life events (SLEs) affected depression in males and only in individuals carrying low-activity MAOA genotype [37]. This evidence concerns the gene MAOA and major depressive disorder.