Age at onset of narcolepsy in two large populations of patients in France and Quebec

Background: Narcolepsy usually starts around adolescence; however, there is great variability in the clinical presentation of narcolepsy. Objective: T o determine the age at onset in conjunction with severity of narcoleptic sy mptoms in two large populations of narcoleptic patients with a similar gene tic background. Methods: Information on age at onset and severity of the co ndition was obtained in 317 patients with well-defined narcolepsy-cataplexy from Montpellier (France) and in 202 from Montreal (Canada). Results: The mean age at onset was 23.4 years in Montpellier and 24.4 in Montreal. The a ge at onset was bimodal in two independent patient populations: a first pea k occurring at 14.7 years, and a second peak occurring at 35. Age at onset clearly differentiates patients with a positive family history of narcoleps y (early onset) from those without a family history. Other clinical and pol ygraphic findings may indicate that young age at onset is associated with i ncreased severity of the condition (higher frequency of cataplexy and decre ased mean sleep latency on the Multiple Sleep Latency Test). Conclusion: Bi modal distribution of age at onset of narcolepsy was found in two independe nt patient populations. Our data suggest that age at onset is genetically d etermined.