BDNF and major depressive disorder: Genes associated with PTSD overlap considerably with those associated with other common psychiatric disorders, such as MDD, alcohol use disorder, bipolar disorder, and schizophrenia [132, 162, 163], including genes involved in the HPA axis, noradrenergic, dopaminergic, and serotonergic systems, and neurotrophins [164, 165] such as BDNF.