Dave I, Estroff B, Gergely T, et al. - Autoimmune disorders develop due to interplay of genetic and environmental factors. Findings from this study lend support to the hypothesis that seasonal variations in exposures during the gestational and/or early postnatal periods could contribute to development of juvenile idiopathic arthritis (JIA).

• From 10,913 children with JIA enrolled at 62 Childhood Arthritis and Rheumatology Research Alliance Registry sites, birth data were obtained and compared with 109,066,226 US births from the same period, to determine if there exists a link between the season of birth and the development of JIA.

• Birth in winter (January–March) was reported in a greater proportion of children with JIA vs the US general population (25.72% vs 24.08%); this finding remained true after stratifying for age of onset (≤ or > 6 yrs).

• Assessment based on the month of birth revealed that a greater proportion of children with JIA were born in January, vs the US population (9.44% vs 8.13%).