Microglial Activation in Narcolepsy Type 1 and Kleine-Levin Syndrome: Positron Emission Tomography (PET) Study in [18F] DPA-714

Formerly known as narcolepsy with cataplexy, narcolepsy type 1 (NT1) is a rare and disabling sleep pathology that affects 0.02% of the population. It occurs mainly in young adults and children, with repercussions throughout their existence. It is characterized by excessive daytime sleepiness (EDS), which is often the most disabling symptom. Diurnal sleep access is irrepressible, typically short-lived, and refreshing. Cataplexies are the most specific, almost pathognomonic sign of this condition. It is a loss of muscle tone in full consciousness, sudden, triggered by an often positive emotion (laugh, excitement, joke). Nighttime sleep is also disturbed and there may be other signs of paradoxical sleep dysregulation such as hypnagogic hallucinations (at sleep) or hypnopompic (waking) hallucinations, and sleep paralysis.

The diagnosis is confirmed by a polysomnographic recording (PSG) followed by iterative sleep latency tests (TILE) the next day. According to the new international criteria (ICSD-3), patients have a sleep latency of less than or equal to 8 minutes to TILE, and at least 2 sleep in paradoxical sleep (ESP) . An ESP during the previous night PSG can replace a TILE ESP. Typical cataplexies must also be found during the interrogation, but a level of hypocretin-1 collapsed in cerebrospinal fluid (CSF) (<110 ng / L) can now be sufficient for diagnosis, given its very high specificity ( 99%) and sensitivity (> 87%) for NT1.

NT1 is due to the selective and irreversible loss of Hcrt neurons. The exact cause of this destruction is still unknown, but the autoimmune hypothesis is strongly favored. The etiology is probably multifactorial, involving genetic and environmental factors. In fact, 97% of patients with NT1 are carriers of the HLA (Human Leukocyte Antigen) allele DQB1 * 06: 02, a class II major histocompatibility complex (MHC) allele.

Treatments of NT1 are currently only symptomatic, targeting the different symptoms: drowsiness, poor sleep at night, cataplexy, and other symptoms related to dysregulation of sleep Microglial activation is involved in the neuroinflammation process of certain central nervous system pathologies.

When microglia are activated, following aggression or cellular inflammation, the expression of TSPO increases. Positron Emission Tomography (PET) is a nuclear imaging technique that can be used to create anatomical and molecular images with high sensitivity. New TSPO-specific tracers have been recently developed, such as [18F] DPA-714, to quantify in vivo microglial activation in brain PET.

The goal here is to study the cerebral microglial activation in PET in NT1 patients with recent evolution (appearance of the first symptoms - somnolence and cataplexy - less than 2 years ago) in comparison with controls; then analyze the effect of age, and the severity of symptoms on this PET imaging biomarker. Thus, we hypothesize microglial activation, particularly of the hypothalamic region, in NT1 patients at an early stage of disease progression, possibly correlated with the severity of symptoms. To test this hypothesis, we will compare the in vivo microglial activation with PET [18F] DPA-714 in NT1 subjects, versus control subjects followed for another age-and-sex-matched non-narcolepsy and hypersomnia-free sleep pathology. The images will be analyzed semi-quantitatively by determining SuVr (or normalized binding value), a method validated in international studies.