We've known for a while that ankylosing spondylitis and its related illnesses tend to run in families. In my case, my grandfather -- who turns 91 next month -- had AS as well, and an uncle had Crohn's disease. A recent study turned to Iceland -- and its small, homogenous population and extensive genealogical database -- to quantify the risk of contracting AS or inflammatory bowel disease if a close relative has it as well.
First-, second-, and third-degree relatives of patients with AS had risk ratios of 94, 25, and 3.5, respectively, indicating an increased risk of developing AS, while first-, second-, and third-degree relatives of patients with IBD had risk ratios for IBD of 4.4, 2.2, and 1.4, respectively. In addition to confirming the genetic risk for AS and IBD independently, the study found elevated cross-risk ratios between IBD and AS in both first- and second-degree relatives. The cross-risk ratios for IBD in first- and second-degree relatives of patients with AS were 3.0 and 2.1, respectively, and, notably, were the very same for AS in first- and second-degree relatives of patients with IBD. Overwhelmingly, findings applied to blood relatives.