Environmental factors in the development of narcolepsy with cataplexy. A case-control study

Introduction. Epidemiological studies suggest the importance of environmental factors in the etiology of narcolepsy-cataplexy in genetically predisposed subjects. Aim. To assess the role of environmental factors in the development of narcolepsy-cataplexy, using a case-control design with control subjects being matched for ethnicity and age. Patients and methods. All patients were recruited through two outpatient clinics at the community of Madrid, ant the diagnosis of narcolepsy fulfilled the criteria of the International Classification on Sleep Disorders-2005. A questionnaire, including 54 environmental psychological stressor life events and 42 infectious diseases items, was administered to 54 patients. We specifically assessed the stressful factors and infectious diseases that occurred in the year preceding the onset of the first symptom of narcolepsy (excessive daytime sleepiness and/or cataplexy). The same questionnaire was administered to 84 control subjects recruited from non-related family members of the same community. Results. Fifty four patients (55.6% males) answered the questionnaire, The mean age at onset of the first symptom was 21.6 +/- 9.3 years, and the mean age at diagnosis was 36.5 +/- 12.4 years. The main finding in narcoleptic patients as compared to control subjects was major changes in the number of arguments with partner, family, or friends' (odds ratio: 5.2; 95% confidence interval: 1.8-14.5). This can be interpreted as having a protective function and it suggests that psychological mechanisms are present since the beginning of the disease. As for the infectious factors, chickenpox was the most frequently reported. No significant differences were found in terms of total numbers of stress-related and infectious factors between cases and controls. Conclusion. Prospective studies regarding the interaction between environmental and genetic factors are warranted.