Epidemiology of juvenile idiopathic arthritis in a multiethnic cohort - Ethnicity as a risk factor

Objective. To study the influence of ethnicity on the risk of developing juvenile idiopathic arthritis (JIA) in a multiethnic community of patients with unrestricted access to health care. Methods. A questionnaire on ethnicity was distributed to all patients with JIA being followed up at the Hospital for Sick Children in Toronto, Ontario, Canada. Of 1,082 patients, 859 (79.4%) responded to the questionnaire. To calculate the relative risk (RR) of developing JIA in this study cohort, the results were compared with data from the age-matched general population of the Toronto metropolitan area (TMA) as provided in the 2001 census from Statistics Canada. Results. European descent was reported by 69.7% of the patients with JIA compared with a frequency of 54.7% in the TMA general population, whereas a statistically significantly lower than expected percentage of the patients with JIA reported having black, Asian, or Indian subcontinent origin. Children of European origin had a higher RR for developing any of the JIA subtypes except polyarticular rheumatoid factor (RE)positive JIA, and were particularly more likely to develop the extended oligoarticular and psoriatic sub-types. A higher frequency of enthesitis-related JIA was observed among patients of Asian origin, while those of black origin or native North American origin were more likely to develop polyarticular RE-positive JIA. Conclusion. In this multiethnic cohort, European descent was associated with a significantly increased risk of developing JIA, and the distribution of JIA subtypes differed significantly across ethnic groups.