Autism Spectrum Disorder and the Risk of Rheumatoid Arthritis: A Matched National Cohort Study

Aims
To test the hypothesis that Autism Spectrum Disorder (ASD) is associated with an increased risk of Rheumatoid Arthritis (RA).
Methods
A matched national cohort study was implemented using Swedish national health registers. Individuals diagnosed with ASD from 1987 to 2017 were identified in the Swedish Patient Register and entered the cohort on the date of their ASD diagnosis. Each individual with ASD was matched to 100 individuals without ASD by sex and birth year. The cohort was followed-up until the youngest age of: an RA diagnosis (in the Patient Register after the age of 18 years), emigration, death, or the end of follow-up on 31-December-2018. The instantaneous relative risk of RA associated with ASD was quantified from Hazard Ratios (HRs) and their associated 95% Confidence Intervals (CI) by fitting Cox proportional hazards regression models.
Results
The cohort comprised 46,164 individuals with ASD (RA(%): 58 (0.13%)), matched with 4,634,895 individuals without ASD (RA(%): 5,484 (0.12%)). Cohort members were followed-up for 0-30 years (median: 6 years), until age from 18 to 67 (median age: 28 years). In the primary analysis, ASD was not statistically significantly associated with all-cause RA (HR=1.06, 95% CI 0.82 - 1.37), seropositive RA (HR=1.00, 95% CI 0.67 - 1.48), or seronegative RA (HR=1.11, 95% CI: 0.79-1.57). Five complementary analyses were consistent with the primary results.
Conclusion
In a large population-based study, individuals diagnosed with ASD did not show an increased risk of rheumatoid arthritis; either seropositive or seronegative.