RT Journal Article SR Electronic T1 Impact of the season of birth on the development of juvenile idiopathic arthritis in the United States: A nationwide registry-based study JF The Journal of Rheumatology JO J Rheumatol FD The Journal of Rheumatology SP jrheum.201238 DO 10.3899/jrheum.201238 A1 Ishaan Dave A1 Brandon Estroff A1 Talia Gergely A1 Christina A. Rostad A1 Lori A. Ponder A1 Courtney McCracken A1 Sampath Prahalad YR 2021 UL http://www.jrheum.org/content/early/2021/06/10/jrheum.201238.abstract AB Objective Autoimmune disorders result from the interplay of genetic and environmental factors. Many autoimmune disorders are associated with specific seasons of birth implicating a role for environmental determinants in their etiopathology. We investigated if there is an association between the season of birth and development of Juvenile idiopathic arthritis (JIA). Methods Birth data from 10,913 children with JIA enrolled at 62 Childhood Arthritis and Rheumatology Research Alliance Registry sites was compared with 109,066,226 US births from the same period using a Chi-square goodness-of-fit test. Season of birth of the JIA cohort was compared to the US population estimate using a two-sided one-sample test for a binomial proportion and corrected for multiple comparisons. Secondary analysis was performed for JIA categories, age of onset, and months of birth. Results A greater proportion of children with JIA were born in Winter (January to March) compared to the US population (25.72% vs 24.08%; pc < 0.0001). This observation was also true after stratifying for age of onset (≤ or > 6 years). When analyzed by the month of birth, a greater proportion of children with JIA were born in January compared to the US population (9.44% vs 8.13%; pc < 0.0001). Conclusion Relative to the general population, children with JIA are more often born in Winter, and specifically the month of January. These observations support the hypothesis that seasonal variations in exposures during the gestational and/or early postnatal periods may contribute to development of JIA.