THE PREVALENCE OF NARCOLEPSY - AN EPIDEMIOLOGIC-STUDY OF THE FINNISH TWIN COHORT

We investigated the prevalence of narcolepsy using a well-defined whit e population previously used for epidemiological investigations: the F innish Twin Cohort. The Cohort consists of 13,888 monozygotic and dizy gotic twin pairs born before 1958. There were 16,179 individuals who p articipated in the study, with a 77.3% response rate. The study method ology included a questionnaire covering sleep and alertness, the Ullan linna Narcolepsy Scale (UNS), a stale specifically developed and teste d for the study, telephone interviews, and finally, clinical evaluatio n, polygraphic recording, and HLA blood typing. Seventy-five subjects were selected for telephone interviews and laboratory evaluations base d on data from both questionnaires. Five of them were strongly suspect ed of narcolepsy, but laboratory data identified only 3. All were dizy gotic (fraternal) twins discordant for the disease with a negative fam ily history and presence of DR2 DQwl (i.e., DRw15 DQw6, new World Heal th Organization classification). The prevalence of narcolepsy in the F innish population is 0.026% (95% confidence interval, 0.0-0.06). This prevalence is lower than that reported in studies performed without po lygraphic recording and is close to that reported in 1945 in the black U.S. population. The tools developed to perform this study, the large st population study of its kind yet performed, can now be used for oth er population investigations.