Narcolepsy without cataplexy differs from the former condition not only in terms of the absence of cataplexy but also in clinical (less severe EDS), biological (low CSF-hypocretin-1 levels in 10–20% of cases) and neurophysiological (lesser increase of REM sleep propensity) characteristics [3], [9]–[11]. This evidence concerns the gene HCRT and narcolepsy.