Incidence and co-occurrence of six autoimmune diseases in childhood: a population-based cohort study in Norway

Autoimmune diseases are among the most common chronic diseases in childhood. We aimed to determine the incidence and co-occurrence of type 1 diabetes, inflammatory bowel disease, juvenile idiopathic arthritis, coeliac disease, autoimmune thyroid disease, and autoimmune liver disease by age and individual-level sociodemographic factors.

In this nationwide, population-based cohort study, we linked individual-level data from the Medical Birth Registry of Norway, Statistics Norway, the Norwegian Prescription Drug Registry, and the Norwegian Patient Registry for all children born in Norway between Jan 1, 2004, and Dec 31, 2020, and who were alive and living in Norway until aged 18 years or until Dec 31, 2024. Cases of diagnosed autoimmune disease (type 1 diabetes, inflammatory bowel disease, juvenile idiopathic arthritis, coeliac disease, autoimmune thyroid disease, and autoimmune liver disease) were identified from ICD-10 codes recorded in the Norwegian Patient Registry. At least two independent diagnostic code registrations were required for valid disease outcomes. Using Cox regression, we examined hazard ratios of the six autoimmune diseases as a co-occurring disease, by primary diagnosis, by region of birth, maternal education, and household income.

Data availability allowed complete analysis of data for 793 772 individuals born between Jan 1, 2007, and Dec 31, 2019. During a mean follow-up from birth to age 11·1 years (range 4·01-17·99), 15 012 autoimmune disease diagnoses were recorded in a total of 14 278 individuals (incidence rate 162·8 [95% CI 160·1-165·5] per 100 000 person-years). 709 (5·0%) individuals received two or three distinct diagnoses of autoimmune diseases by age 18 years. Statistically significant co-occurrence was observed between all autoimmune diseases examined, except for between inflammatory bowel disease and type 1 diabetes and between inflammatory bowel disease and autoimmune thyroid disease. The incidence of a co-occurring autoimmune disease was highest among individuals with autoimmune liver disease (65 [41·4%] of 157 cases). We found regional variation in incidence, with higher incidence in northern Norway compared with southern Norway for juvenile idiopathic arthritis (adjusted hazard ratio [HR] 1·83 [95% CI 1·55-2·15]), inflammatory bowel disease (1·52 [1·27-1·82]), and type 1 diabetes (1·14 [1·02-1·28]). Higher maternal education was associated with a reduced incidence of type 1 diabetes (HR 0·90 [95% CI 0·81-1·00]) and autoimmune thyroid disease (0·84 [0·72-0·98]), and a higher incidence of coeliac disease (1·45 [1·34-1·58]). Higher household income was associated with a reduced incidence of autoimmune thyroid disease (HR 0·85 [95% CI 0·72-0·99]) and a higher incidence of coeliac disease (1·63 [1·50-1·76]).

Increased awareness of the risk of co-occurring autoimmune diseases in childhood is warranted by patients, clinicians, and health systems. Regional and socioeconomic differences warrant further research for potential common early-life risk factors.

South-Eastern Norway Regional Health Authority.