Orexin/hypocretin research began in 1998, as a result of the discovery of a newhypothalamic neuropeptide. In 1999, it was found that mutations in the orexin/hypocretin-related genes caused a sleep disorder (narcolepsy) in dogs and mice.These findings were soon followed by the discoveries of orexin/hypocretin liganddeficiency in human narcolepsy.