For example, hypothetically, if a patient with endogenous depression was severely burned and his/her house burnt to ashes, losing all his/her fortune, this depressive condition could be expressed as a set of depressive states, incorporating peripheral (TPH1 dysfunction, TDO activation, IDO activation) and central (TPH2 activation, KMO activation) determinants. The gene discussed is IDO1; the disease is major depressive disorder.