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HCRT1 and HCRT2 have respective receptors, named HCRT1 R and HCRT2 R. These two peptides are encoded by a precursor protein called pre-pro-hypocretin. HCRT1 (orexin-A) and HCRT2 (orexin-B) are produced exclusively by ~ only 70,000 neurons located in the lateral and posterior hypothalamus. The hypocretins (also known as orexins) are two peptides that were identified in the brain in 1998. Children with NC have a particular phenotype with movement disorders, early puberty, and weight gain. In addition, patients with NC experience dream-enacting behaviors associated with increased muscle tone during REM, a parasomnia termed RBD. NC is associated with abnormalities of REM sleep regulation consisting in complete or partial intrusions of this stage into wakefulness, resulting into episodes of irresistible sleepiness, cataplectic events, sleep paralysis, and hypnagogic hallucinations. The risk of a first-degree relative developing NC is 10–40 times higher (1–2%) than in the general population. More than 95% of the cases are sporadic but the disease has been described in some families and in monozygotic twins. NC affects men and women equally and symptoms persist throughout lifetime. Symptoms usually begin during adolescence or early adulthood but onset during childhood is not exceptional. NC is a rare disease with a prevalence rate of 0.02–0.20% worldwide and ~ 30 cases per 100,000 inhabitants in Europe, Canada and the United States. Car accidents and social, familial, professional, and psychological problems are common and can markedly impact the quality of life, particularly due to severe EDS.
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It is a neurological disease clinically characterized by severe and irresistible episodes of EDS, cataplexy (sudden onset of muscle paralysis triggered by strong emotions with retained consciousness), sleep paralysis, hypnagogic and hypnopompic hallucinations, automatic behaviors, fragmented nocturnal sleep, RBD, and weight gain. Narcolepsy with cataplexy (NC) (also known as narcolepsy type 1) is a chronic sleep disorder of autoimmune origin characterized by dysregulation of REM sleep secondary to impaired hypocretin (HCRT) neurotransmission in the brain.
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This review does not cover neurological and systemic autoimmune diseases where sleep abnormalities are not common such as neuromyelitis optica, myasthenia gravis, systemic lupus erithematosus, and Sjögren’s syndrome. This article reviews the sleep disorders that have an immunological pathogenesis (narcolepsy and anti-IgLON5 disease) and neuroimmunological disorders that show sleep abnormalities (MS, Guillain–Barré syndrome, and paraneoplastic neurological syndromes (PNS)). Factors involved may be related to (1) a direct causal effect between autoimmune cellular or humoral mechanisms and sleep disorders/symptoms, (2) common risk factors between autoimmune diseases and sleep conditions, increasing their association, (3) typical symptoms of autoimmune diseases exerting an effect on sleep regulatory mechanisms (e.g., fatigue in MS), (4) effects of treatment (e.g., steroids inducing insomnia) other related medical factors (e.g., hospitalization in Guillain–Barré Syndrome), and (5) a coincidental association between autoimmune diseases and highly prevalent comorbid sleep disorders (e.g., insomnia). The association between autoimmune diseases and sleep symptomatology and sleep disorders is complex and multifactorial.