Résumé
In summary, deficient hypocretin-1 transmission is highly specific and sensitive for sporadic narcolepsy with typical excessive daytime somnolence, cataplexy and HLA DQB1*0602 allele. Hypocretin ligand deficiency appears not to be the major cause for other hypersomnias but a pathophysiological continuum between narcolepsy without cataplexy and idiopathic hypersomnia could be hypothesized. Undetectable CSF hcrt-1 levels are highly sensitive and specific for narcolepsy and are a useful diagnostic tool for pediatric and atypical cases. A decreased level however should not systematically suggest the diagnosis of narcolepsy. Indeed, low levels can be observed in various neurological conditions: neuroimmune disorders such as Guillain Barré syndrome and Miller Fisher syndrome; neurological conditions associated with lesion or dysfunction of the lateral hypothalamus; advanced forms of Parkinson disease. Finally, exploring the hypocretins in neuropsychiatric disorders is a growing field that requires further investigation to understand the role of hypocretins in pathology. The evaluation methods of the hypocretinergic system needs also to be improved with other techniques in order to evaluate the functioning of hypocretin-1 or 2 receptors as well as the consequences of partial lesions of hypocretin cells without low CSF hypocretin-1. Measurement and interpretation of intermediate and high levels of hypocretin, as reported in restless legs syndrome for example, requires more study.