HCRTR2 and Cataplexy: Prepro-orexin knockout mice, orexin neuron-ablated (orexin/ataxin-3-transgenic) mice, and OX1R/OX2R double knockout mice showed highly similar phenotypes to the human condition, characterized by behavioral arrests similar to cataplexy, occasional direct transitions to REM sleep from wakefulness, and highly fragmented sleep-wake cycles (Chemelli et al., 1999; Hara et al., 2001; Mochizuki et al., 2004).