Narcolepsy type 1: an environment-influenced disease

Narcolepsy type 1 (NT1) is a chronic and non-progressive neurological disorder that frequently arises in childhood. NT1 is characterized by loss of physiological boundaries between wakefulness and sleep, excessive daytime sleepiness, cataplexy, sleep paralysis, and hypnagogic or hypnopompic hallucinations. Current evidence supports a complex multifactorial model in which NT1 results from the interplay of immune-related genetic predisposition and environmental triggers, leading to immune-mediated destruction or dysfunction of hypocretin-producing neurons. Accordingly, we aimed to provide an updated review of the evidence regarding the role of environmental factors in the etiopathogenesis of NT1.

We performed a literature search in PubMed and Scopus databases up to April 22, 2026, to retrieve publications about NT1 disease concordance in monozygotic twins and about its environmental risk factors.

Selected studies described disease concordance in 8 out of 24 monozygotic twin pairs (33%), and differences between NT1 discordant twins with reference to body mass index and weight changes, history of head trauma, infectious exposures, and comorbidities. Among the studies that investigated environmental risk factors for NT1, season of birth, the 2009 pandemic influenza A/H1N1 infection and related vaccination, toxins, and gut microbiota alterations were reported as potential determinants.

Overall, evidence from twin studies and epidemiologic studies suggests that environmental factors play a role in NT1. However, the limited number of studies and their methodological limitations preclude a comprehensive assessment of these potential etiological factors, highlighting the need for further investigation.