HCRT and narcolepsy: While most individuals with narcolepsy without cataplexy exhibit normal CSF orexin concentrations (Dauvilliers, Baumann, et al. 2003), a subset of NT2 patients has been reported to have orexin neuron loss below 50% of normal levels, a pattern also observed in rodent studies (Thannickal et al. 2009; Black et al. 2018).