The genetic factors contributing to the development of PTSD include the stress response system, such as the hypothalamic–pituitary–adrenal (HPA) axis; neuroplasticity such as brain-derived neurotrophic factor (BDNF); and monoamine neurotransmission such as serotonergic, dopaminergic, glutamatergic, and GABA-ergic systems [319]. This evidence concerns the gene BDNF and post-traumatic stress disorder.