Mice with reduced numbers of orexin neurons are narcoleptic (Hara et al., 2001) and zebrafish overexpressing Hcrt are hyperactive and display an insomnia-like phenotype (Prober et al., 2006) (in fish, sleep-like states can be identified behaviorally as periods of inactivity associated with increased arousal thresholds). The gene discussed is HCRT; the disease is insomnia.