Elevated circulating cell-free mitochondrial DNA level in cerebrospinal fluid of narcolepsy type 1

Narcolepsy type 1 (NT1) is a rare neurological disorder characterized by excessive daytime sleepiness and cataplexy, thought to result from an autoimmune process targeting the hypothalamic hypocretin-producing neurons. Aiming to add clues to the latter hypothesis, we investigated circulating cell-free mitochondrial DNA (ccf-mtDNA) levels in cerebrospinal fluid (CSF), a possible biomarker for neurodegeneration, neuroinflammation or immune activation, from 46 NT1 patients with low CSF hypocretin-1, compared with 32 controls. We found significantly increased ccf-mtDNA levels in NT1 patients compared with controls, which negatively correlated with CSF hypocretin-1 concentrations. Additionally, higher ccf-mtDNA levels were observed in patients with elevated number of sleep onset rapid eye movement periods. These observations imply that increased levels of ccf-mtDNA associate with reduced CSF hypocretin-1 concentrations leading to greater alteration in sleep architecture. Furthermore, cytokine profiling in CSF revealed significant changes in interleukins 6 and 18 in NT1 patients, suggesting an active neuroinflammatory process possibly linked to ccf-mtDNA release, thus pointing to a specific inflammatory signature in NT1. These findings hint a potential mitochondrial dysfunction and neuroinflammation in NT1. Further studies are needed to elucidate the underlying mechanisms and how this may reflect on therapy.