Narcolepsy among first- and second-generation immigrants in Sweden: A study of the total population

To study incident narcolepsy in first- and second-generation immigrant groups using Swedish-born individuals and native Swedes as referents.

The study population included all individuals registered and alive in Sweden at baseline. Narcolepsy was defined as having at least one registered diagnosis of narcolepsy in the Swedish National Patient Register. The incidence of narcolepsy in different immigrant groups was assessed by Cox regression, with hazard ratios (HRs) and 95% confidence intervals (CI). The models were stratified by sex and adjusted for age, geographical residence in Sweden, educational level, marital status, co-morbidities, and neighbourhood socioeconomic status.

In the first-generation study, 1225 narcolepsy cases were found; 465 males and 760 females, and in the second-generation study, 1710 cases, 702 males and 1008 females. Fully adjusted HRs (95% CI) in the first-generation study was for males 0.83 (0.61-1.13) and females 0.83 (0.64-1.07), and in the second-generation study for males 0.76 (0.60-0.95) and females 0.91 (95% CI 0.76-1.09). Statistically significant excess risks of narcolepsy were found in first-generation males from North America, and second-generation males with parents from North America, and second-generation females with parents from Latin America.

There were only significant differences in incident narcolepsy between native Swedes and second-generation male immigrants. The observed differences can partly be explained by differences in Pandemrix® vaccinations and are probably not attributable to genetic differences between immigrants and natives.