Severity of narcolepsy among French of different ethnic origins (South of France and Martinique)

Study objectives: The aim of the study was to describe the clinical and polygraphical characteristics of narcoleptics, with and without cataplexy and to assess HLA predisposition across two different ethnic populations. Design and Setting: Patients were 126 men and 58 women referred to the Montpellier Sleep Disorders Center (Mtp) and 12 men and 8 women referred to the Fort-de-France Sleep Disorders Center (FdF) (Martinique, a French West Indy island) with symptoms of narcolepsy. Participants: Narcoleptics were included if they had both excessive daytime sleepiness and clear-cut cataplexy (for the group with cataplexy), a mean sleep latency of less than 8 minutes and at least two sleep onset REM periods. Interventions: N/A Measurements and Results: Narcolepsy without clear-cut cataplexy was rare (12/172) in the Mtp population whereas it was as frequent as full-blown narcolepsy (10/10) in the FdF population. Comparison between narcoleptics with cataplexy from the Mtp and FdF populations revealed a younger age of onset, a trend towards more severe sleepiness and lower frequency of cataplexy in Martinicans. Comparison between narcoleptics without cataplexy from the Mtp and FdF population revealed a higher frequency of hypnagogic hallucinations and sleep paralysis and a trend towards more severe sleepiness in Martinicans. 4.2% of the Mtp and 15% of the FdF patients were negative for HLA DR2. However all of them were positive for HLA DQ1. Moreover, a tight association with HLA DRB1 *1503 was observed in Martinicans in contrast with DRB1*1501 in the Mtp population. Association with HLA DQB1 *0602 was observed in 99.4% of narcoleptics with cataplexy and in 89.5% of those without cataplexy. Conclusions: Narcolepsy is a heterogeneous clinical syndrome, the moreso as ethnic origins are considered. A modulating effect of HLA and non-HLA genes on symptoms disease may explain these differences.