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RESEARCH PRODUCT

Season of birth effect in narcolepsy

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The causes of narcolepsy are unknown.1 Genetic factors such as positivity for HLA DR2 or certain genotypes of tumor necrosis factor–alpha or the orexin gene only explain a fraction of the risk. A season of birth effect has been observed in numerous studies for schizophrenia and bipolar disorder with a 10% excess of birth in winter and spring.2 Among the underlying factors discussed are infectious agents as well as seasonal variations in nutrition, light effects, and toxins.2 Most recently, the vitamin D hypothesis has been revisited.3 The production of vitamin D is associated with exposure to sunlight and the active 1,25 dihydroxyvitamin D3 is a potent modulator of immune functions,4 a dysfunction of which is presumably important before the onset of narcolepsy.1 Recently, a non significantly deviated pattern of birth rates in American narcoleptic patients was reported, …