According to the Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-5) currently being finalized, syndromes with primary hypersomnolence can be practically divided into 3 groups: 1) narcolepsy caused by hypocretin (orexin) deficiency, a disorder associated with Human Leukocyte Antigen (HLA) marker DQB1*06:02 and believed to be autoimmune (almost all cases with cataplexy), 2) Kleine-Levin Syndrome (KLS), and 3) syndromes with hypersomnolence unexplained by hypocretin abnormalities (generally without cataplexy) [1]. The gene discussed is HCRT; the disease is mental disorder.