Title

Environmental Risk Factors for Narcolepsy

Date of Award

2005

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Psychology

First Advisor

John R. Harsh

Advisor Department

Psychology

Abstract

There is a general consensus that the etiology of narcolepsy involves both genetic and environmental risk factors. However, there has only been one previous case-control study on environmental risk factors, which focused exclusively on the dichotomous assessment of psychological stressors that occurred within one year prior to symptom onset. This study sought to examine the effect of a variety of environmental risk factors throughout the lifespan prior to symptom onset. Cases (n = 63) were recruited through the Stanford Center for Narcolepsy. All were HLA-DQB1*0602 positive, met conventional MSLT criteria, and reported typical cataplexy. Controls (n = 63) were non-related family members of cases and local community members. Controls were frequency matched on current age to minimize recall bias and reported on events prior to the age of 20 since this is the median age of cataplexy onset. The procedure entailed mailing a self-administered questionnaire that assessed the frequency and age of each risk factor. Portions of this questionnaire (The Narcolepsy Environmental Triggers Survey) were previously assessed for reliability and validity while other portions were derived from published recommendations on the questionnaire assessment of environmental risk factors. A small minority of the infectious diseases that were examined carried a significant risk. These were flu infections (OR = 1.79, p < .05) and unexplained fevers (OR = 3.89, p < .05). Several of the psychological stressors that were examined carried a significant risk. These included major changes in sleeping habits (OR = 2.01, p < .05), which replicates previous research. Interestingly, total stressors before the age of 10 was a significant risk factor (OR = 1.16, p < .05). These findings indicate the importance of environmental risk factors in the etiology of narcolepsy. The timing of these risk factors may also be significant given the risk associated with exposure prior to an age where puberty typically begins and given the post-pubertal onset of narcolepsy. Any future research must take environmental factors into account if a complete understanding of the etiology of narcolepsy is to emerge.