Pediatric Rheumatology Online Journal → June 2003 → Epidemiology, Classification, Immunology and Immunogenetics → Abstract #2

JUVENILE IDIOPATHIC ARTHRITIS IS NOT ASSOCIATED WITH BIRTH ORDER

S. Prahalad,1 A. Fraser,2 E. O'Brien,2 R. Kerber,2,3 G. Mineau,2,3 J. Bohnsack.1

1Pediatrics, U of Utah SOM, Salt Lake City, UT; 2Huntsman Cancer Institure, U of Utah, Salt Lake City, UT; 3Dept of Oncological Sciences, U of Utah, Salt Lake City, UT

Objectives: Several diseases including multiple sclerosis, type 1 diabetes, ankylosing spondylitis and rheumatoid arthritis have been reported to be associated with birth order, suggesting that intrauterine or early childhood environmental factors might influence disease susceptibility. We aimed to determine if there was an association between birth order and juvenile idiopathic arthritis (JIA).
Methods: Patients with JIA in a clinical database were linked with records in the Utah Population Database (UPDB), a computerized genealogy database of over 6 million records. For each linked case, ~10 controls matched on sex and birth year were selected. Information on birth order, sibship size and maternal age at delivery was obtained from UPDB. Chi-squared analysis was used to examine if JIA was more prevalent among different birth orders compared to controls.
Results: A total of 333 cases and 3295 controls were analyzed. The mean (SD) birth order among cases and controls were 2.5 (1.7) and 2.6 (1.7) respectively. The mean (SD) sibship sizes were 3.6 (2.0) and 3.6 (1.9) respectively. Mean (SD) maternal age was 26.9 (5.8) and 25 (7.8) years respectively. When cases and controls were stratified by sibship size, the distribution of the birth orders and total sibship sizes were similar in both groups. After excluding families with only one child, the proportion of first-born children among the cases and controls was not statistically significantly different (86/311 vs. 717/2978; p = 0.18). The proportion of last-born children was also not different (120/311 vs. 1184/2978; p = 0.63). There were also no differences when cases with early onset oligoarthritis or enthesitis related arthritis were analyzed separately.
Conclusions: Using a robust dataset and a large cohort of appropriately matched controls, we were unable to show a statistically significant association between birth order and juvenile idiopathic arthritis.