Narcolepsy with Cataplexy Linked to Degeneration of Both Hypocretin and Locus Coeruleus Neurons

Narcolepsy type 1 (NT1), characterized by hypocretin deficiency, is a debilitating sleep-wake disorder. Previous research primarily linked NT1 with the loss of hypothalamic hypocretin (orexin) neurons, often implicating an autoimmune etiology due to associations with HLA-DQB1*06:02 and CD4+ T-cell infiltration. However, the full extent of neuronal degeneration beyond hypocretin neurons and the precise mechanisms driving this loss remained incompletely understood. This study investigates other brain regions potentially affected in NT1 pathophysiology.

Researchers conducted a post-mortem neuropathological analysis on 11 brains from individuals diagnosed with narcolepsy with cataplexy. They specifically quantified the number and size of norepinephrine neurons in the locus coeruleus (LC) and observed microglial clustering around both hypocretin and noradrenergic neurons. The study aimed to identify additional neuronal populations affected in narcolepsy beyond the previously established hypocretin system.

Individuals with narcolepsy with cataplexy exhibited an average 46% loss in the number of brainstem norepinephrine neurons within the locus coeruleus (LC). This significant neuronal loss was accompanied by an 18% increase in the size of the remaining LC noradrenergic neurons. Furthermore, microglial clustering was observed around both the degenerating hypocretin neurons in the hypothalamus and the noradrenergic neurons in the locus coeruleus. This microglial presence strongly suggests an active inflammatory or immune-mediated process contributing to the degeneration of both neuronal populations in narcolepsy with cataplexy. These findings expand the neuropathological understanding of narcolepsy beyond the sole involvement of hypocretin neurons.