Clinical meaning
Narcolepsy is a chronic neurological disorder of sleep-wake regulation caused by the loss of orexin-producing (hypocretin-producing) neurons in the lateral hypothalamus. Orexin is a neuropeptide that plays a critical role in maintaining wakefulness and regulating transitions between sleep and wake states. In narcolepsy type 1 (formerly narcolepsy with cataplexy), approximately 90% of orexin-producing neurons are destroyed, most likely through an autoimmune process. This results in profoundly low or undetectable cerebrospinal fluid (CSF) orexin levels (less than 110 pg/mL). Narcolepsy type 2 (without cataplexy) may involve partial orexin loss or dysfunction without complete neuronal destruction. Normal sleep architecture follows a predictable pattern: wakefulness transitions to non-rapid eye movement (NREM) sleep through stages N1, N2, and N3, followed by rapid eye movement (REM) sleep approximately 90 minutes after sleep onset. In narcolepsy, the loss of orexin destabilizes the boundaries between wake and sleep states, causing the brain to transition rapidly and inappropriately into REM sleep. This explains the hallmark features of narcolepsy: patients may enter REM sleep within minutes of falling asleep (sleep-onset REM periods, or SOREMPs), and elements of REM sleep...