Huntington's disease among immigrant groups and Swedish-born individuals: a cohort study of all adults 18 years of age and older in Sweden.

BACKGROUND: There is a lack of studies of Huntington's disease (HD) in immigrants. OBJECTIVE: To study the association between country of birth and incident HD in first-generation immigrants versus Swedish-born individuals and in second-generation immigrants versus Swedish-born individuals with Swedish-born parents. METHODS: Study populations included all adults aged 18 years and older in Sweden, i.e., in the first-generation study 6,042,891 individuals with 1034 HD cases and in the second-generation study 4,860,469 individuals with 1001 cases. HD was defined as having at least one registered diagnosis of HD in the National Patient Register. The incidence of HD in different first-generation immigrant groups versus Swedish-born individuals was assessed by Cox regression, expressed as 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, and neighborhood socioeconomic status. RESULTS: Mean age-standardized incidence rates per 100,000 person-years were for all Swedish-born 0.82 and for all foreign born 0.53 and for all men 0.73 and for all women 0.81, with the highest incidence rates for the group 80-84 years of age. After adjusting for potential confounders, the HRs were lower in women in the first- and second-generation, i.e., 0.49 (95% CI 0.36-0.67) and 0.63 (95% 0.45-0.87), respectively, and also among women from Finland or with parents from Finland. SIGNIFICANCE: In general, the risk of HD was lower in first-generation and second-generation immigrant women but not among male immigrants.