Cohort profile: systemic lupus erythematosus in Sweden: the Swedish Lupus Linkage (SLINK) cohort

PURPOSE: A cohort of individuals with systemic lupus erythematosus (SLE) was identified through linkage of several national registers to investigate important epidemiological questions using not only population-based data to minimise selection bias, but also to identify matched comparators from the general population to serve as controls. This cohort was established to overcome the general dearth of data in SLE epidemiology. PARTICIPANTS: All individuals registered in Sweden with a personal identity number and who have obtained medical care at any hospital or public non-primary outpatient specialist care with suspected SLE were identified. Inpatient register data date back to the 1960s, although complete national coverage of the inpatient register was achieved in 1987. In 2001, the outpatient component was also added to the register, representing the entire country of Sweden. For each suspected individual with SLE, up to five individuals from the general population were identified and matched on sex, birth year and county of residence. FINDINGS TO DATE: We have linked this study population to a number of national and quality registers in Sweden to identify first-degree relatives, deaths, births, dispensed prescriptions, comorbidities and disease end points, such as stroke and cancer, as well as basic health economic data. We found geographic variability in the prevalence of SLE by county. We have also shown that being first-born confers a reduced odds of having SLE in childhood and early adulthood. FUTURE PLANS: In addition to updating the national register linkage with several more years of follow-up data, we are adding several quality registers in Sweden, including the Tuberculosis register and the Social Insurance Office database. While these updates are ongoing and additional follow-up accumulates, we are studying a number of outcomes in SLE, including stroke, pregnancy and death. We will continue to present findings at scientific conferences and in the peer-reviewed literature.