Substantially lower frequency of cataplexy in OX2R−/− mice as compared to orexin−/− mice appears to be inconsistent with the fact that mutations of OX2R gene are solely responsible for an inherited canine model of narcolepsy, which demonstrate frequent occurrence of cataplexy as well as excessive sleepiness (Lin et al., 1999). The gene discussed is HCRT; the disease is narcolepsy.