Investigators may have uncovered the perinatal and early-life risk factors associated with an increased likelihood of developing ankylosing spondylitis, according to an article published by Morin et al in RMD Open. Investigators used the Swedish National Patient Register to identify 5,612 patients with ankylosing spondylitis and 22,042 controls. They then validated their findings in a further analysis comparing 3,965 patients with ankylosing spondylitis and 6,070 siblings without the disease. Patients who had older siblings (adjusted odds ratio [OR] = 1.12, 95% confidence interval [CI] = 1.04–1.22) and a history of childhood tonsillectomies (adjusted OR = 1.30, 95% CI = 1.13–1.49) were at a heightened risk of developing ankylosing spondylitis in both analyses. They reported no statistically significant associations between fetal growth–related factors or perinatal factors and the risk of developing the disease. The investigators concluded that childhood infections may play a role in the etiology of ankylosing spondylitis.