For example, the knockout of hypocretin/orexin (hcrt/orx) produces narcolepsy (Chemelli et al., 1999), making hcrt/orx the first peptide messenger known to be essential for normal wakefulness and for environment-appropriate switches in the states of consciousness in mammals (De Lecea et al., 2006; Sakurai, 2007). This evidence concerns the gene HCRT and narcolepsy.