Objective: Narcolepsy is a chronic sleep disorder long hypothesised to be an autoimmune disease. Complement-mediated immune mechanisms have not been investigated in detail in narcolepsy. Our aim was to establish the significance of classical pathway activation in narcolepsy. Methods: Sera of 42 narcolepsy patients and 26 healthy controls were screened with ELISA to determine the levels of C1q, C3a, C4d and complement component 4 binding protein (C4BP). A home-made ELISA method was developed to detect antibodies to C4BP-alpha (anti-C4BPA). The correlation between complement levels and clinical findings was examined. Results: C1q levels were significantly higher in narcolepsy patients while C4d and C4BP levels were significantly lower compared to healthy controls. C3a levels were comparable among patients and controls. Eleven narcolepsy patients showed serum anti-C4BPA levels. Total rapid eye movements (REM) time, sleep onset latency, REM sleep latency, sleep activity, percentage of wakefulness after sleep onset and Epworth sleepiness scale scores were correlated with levels of different complement factors. Conclusion: Complement-mediated immune mechanisms might partake in narcolepsy pathogenesis. The precise role of autoantibodies on complement level alterations needs to be investigated. Levels of complement factors and degradation products may potentially be utilised as biomarkers to predict the clinical severity of narcolepsy.

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Morvan syndrome (MoS) is typically characterized by neuromyotonia, sleep dysfunction, dysautonomia, and cognitive dysfunction. However, MoS patients with mild peripheral nerve hyperexcitability (PNH) or encephalopathy features have been described. A 46-year-old woman presented with a 2-month history of constipation, hyperhidrosis, and insomnia. Neurologic examination revealed muscle twitching and needle electromyography showed myokymic discharges in all limbs. No clinical or electrophysiological features of neuromyotonia were present. Although the patient denied any cognitive symptoms, neuropsychological assessment revealed executive dysfunction, while other cognitive domains were preserved. Cranial and spinal MRIs were unrevealing and tumor investigation proved negative. Polysomnography examination revealed total insomnia, which was partially reversed upon immune-modulatory therapy. Investigation of a broad panel of antibodies revealed serum leucine-rich glioma inactivated protein 1 and contactin-associated protein 2 antibodies. The features of this case indicate that the presentation of PNH syndromes may show significant variability and that MoS patients may not necessarily exhibit full-scale PNH and encephalopathy symptoms.

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