Links between orexin and amyloid processes have been underlined recently. During the Alzheimer's process an upregulation of the orexin mechanism has been observed. The pathophysiological mechanism of narcolepsy type 1 is linked to orexin deficiency. Thus, the investigators hypothesized that patients with narcolepsy may be protected from amyloid brain lesions, hallmarks of the Alzheimer's process. To test this hypothesis, the investigators analyzed the brain amyloid load measured by PET-scan amyloid brain imaging in patients with narcolepsy type 1 compared to controls without cognitive deficits.

The lack of innovative treatments in Alzheimer' disease (AD) is due to the non-understanding of the pathological process. The investigators need to include the latest concept of the sleep-wake/circadian kinetics of proteins in the brain, the new theory of the wash-out of pathological proteins via the brain glymphatic system during sleep and act at an early stage. New pathways are opened to better understand proteinopathies' processes and to propose new therapeutics interventions. The variations of the production/clearance curves of amyloid in the cerebrospinal fluid (CSF) during circadian rhythms and sleep-wake cycles have been demonstrated in in vivo metabolism experimentations. Suprachiasmatic nucleus damages due to AD may induce circadian regulation dysfunction and secondary sleep/wake cycle alterations. Key sleep/wake cycle neuromediators (Orexin-A, melatonin) are involved in the regulation of brain amyloid levels. The influence of orexin-A signaling on Aβ metabolism in animals and humans was recently highlighted. In rats, orexin-A release shows a 24-h fluctuation similar to that of brain interstitial fluid Aβ. In transgenic mice that overexpress amyloid precursor protein (APP), brain interstitial fluid Aβ concentration increases during wakefulness and after orexin-A infusion. Conversely, it decreases during sleep and after infusion of an orexin-A receptor antagonist6. In transgenic mice that overexpress APP/presenilin1 (PS1), in which the orexin gene is knocked out, a reduction of Aβ pathology was found, possibly caused by changes in sleep time. Orexin-A is linked to Aβ42 in AD and an increase of CSF orexin-A is observed in AD vs. controls, possibly related to sleep deterioration and neurodegeneration.

The narcolepy with cataplexy type 1 is the only disease with a specific orexin deficiency. Montpellier team have previously underlined in 15 patients with narcolepsy type 1 a normal level of Aβ42 in the CSF. The clinical expertise of the narcolepsy center suggested that the frequency of AD in old narcoleptic patients is low. The hypothesis was that patients with narcolepsy type 1 may be protected from amyloid brain lesions, hallmarks of the Alzheimer's process. The objective was to determine whether the brain amyloid load by PET-scan18 F-AV-45 measured with a semi-quantitative analysis (mean cortical SuVr) is lower in patients with narcolepsy type 1 older than 65 years-old than in cognitively normal age- and gender-matched controls.

Inclusion criteria:

Narcolepsy group:

• Patients with narcolepsy type 1 older than 65 y.o. with orexin deficiency as required by international diagnosis criteria (ICSD3) with a follow-up in the national reference center for narcolepsy;
• Treated or not with psychostimulant drugs in relation to disease symptoms;
• Patients with CSF samples available or with scheduled lumbar puncture for diagnosis purpose;
• No contra-indications of the PET-scan18F-AV-45
• With a free and informed consent to participate to the study.

Control group:

• Subjects already included in the MEMENTO-AMYging and/or MAPT-AV45 ancillary studies in the memory center with normal cognitive tests after neuropsychological assessments especially in the episodic memory tests and the brain amyloid PET-scan18F-AV-45 data with SuVr measurements.

Exclusion criteria:

• Controls subjects or patients without free and informed consent to participate to the study
• No PET-scan18F-AV-45 data available
• No CSF samples
• Pathologies being life-threatening in a short term
• Patients deprived of freedom by court or administrative order
• Patients living in institution
• Major protected by the Law.