Anti-NMDA receptor encephalitis, associated with ovarian teratomas and small-cell lung cancer, presents as agitation, paranoia, auditory hallucinations, and fluctuating cognitive impairment, whereas autoantibodies associated with anti-Hu and anti-Ma2 in small-cell lung carcinoma and testicular germ cell tumors are characterized by depression, amnesia, and rigidity in behavior. The gene discussed is PNMA2; the disease is small cell lung carcinoma.