The distribution and frequencies of APOE genotypes in AD also differ from those of patients with anxiety (P < 0.001), depression (P < 0.001), psychosis (P < 0.005), migraine (P < 0.03), vascular encephalopathy (P < 0.001), and posttraumatic brain injury syndrome (P < 0.03). The gene discussed is APOE; the disease is major depressive disorder.