Incidence and genetic risk of juvenile idiopathic arthritis in Norway by latitude.

We aimed to investigate the incidence of juvenile idiopathic arthritis (JIA) in the three geographical regions of Norway, and whether potential regional incidence differences are explained by environmental or genetic factors across regions. We conducted a register-based cohort study including all Norwegian children born 2004-2019, with follow-up throughout 2020. The JIA diagnosis defined by ≥ 2 ICD-10 codes for JIA was validated against medical records. The incidence rate (IR) and hazard ratio (HR) for JIA were estimated for all Norway, and for the regions North, Mid, and South. In a sub-sample from the Norwegian Mother, Father, and Child Cohort Study (MoBa), the genetic risk for JIA was assessed in the three regions. After median 9.1 (range 0.3-16.0) years of follow-up, we identified 1184 JIA cases and 910058 controls. The IR for JIA/100 000 person-years was 14.4 in all of Norway; 25.9 in region North, 17.9 in region Mid and 12.5 in region South. The HR (95% CI) of JIA in region North was 2.07 (1.77-2.43) and in region Mid 1.43 (1.23-1.67) compared to region South. Adjustments for perinatal factors, socioeconomic status, and early antibiotic exposure did not change our estimates substantially. In MoBa (238 cases, 57392 controls), the association between JIA and region of birth was no longer significant when adjusting for genetic factors. We found a higher incidence of JIA with increasing latitude, without evidence for available environmental factors explaining the observed gradient. In contrast, genetic factors modified the association, but further studies are warranted.

Informations de copyright

This article is protected by copyright. All rights reserved.