Sleepiness that cannot be overcome: narcolepsy and cataplexy

Narcolepsy-cataplexy syndrome is characterized by excessive daytime sleepiness, cataplexy, sleep paralysis, hypnagogic hallucinations and disturbed nocturnal sleep. It is strongly associated with the genetic marker, human leucocyte antigen (HLA) DQB1*06:02. A deficit in the endogenous hypocretin/orexin system due to neuronal degeneration in the lateral hypothalamus, induced by an autoimmune-mediated process, is the primary pathophysiology associated with the human disease. The important finding of an association with hypocretin genes in animal models of narcolepsy has led to the establishment of cerebrospinal fluid hypocretin measurements as a new diagnostic test for human narcolepsy. This is a fascinating story of translation of basic science research into clinical practice in sleep medicine during the past decade. Recent advances have shed light on the associations between respiratory medicine and narcolepsy-cataplexy research. The first is that upper airway infections, including H1N1 and/or streptococcal infections, may initiate or reactivate an immune response that leads to loss of hypocretin-secreting cells and narcolepsy in genetically susceptible individuals. The second is that an increased incidence of sleep disordered breathing among narcoleptic subjects may relate to the impairment of central control of breathing, linked to hypocretin deficiency or carriage of HLADQB1*06:02, in animals and human subjects with narcolepsy, respectively, indicating neural dysfunction in an area where respiratory and sleep-wake systems are closely interrelated.