In the meta-analysis conducted by Elwood et al. [45], a positive correlation was found between the occurrence of postnatal depression symptoms in the mother and polymorphisms of the HMNC1, COMT, MAOT, PRKCB, ESR1, and SLC6A4 genes and the presence of life events considered stressful. This evidence concerns the gene SLC6A4 and depressive symptom measurement.