HCRT and narcolepsy: Several studies have confirmed reduced cerebrospinal fluid (CSF) histamine levels in human narcolepsy especially in hypocretin-deficient narcolepsy [60,61,62], while a recent study reported that narcoleptic children with hypocretin deficiency had a higher CSF histamine level together with a lower t-MH level leading to a decreased histamine turnover and an impairment of histaminergic neurotransmission [63].