The Relative Risk of Inflammatory Bowel Disease Among Parents and Siblings of Crohnʼs Disease Patients

Siblings of patients with Crohnʼs disease are 17–35 times more likely to develop the disease than members of the general population. Parents of patients with Crohnʼs disease are 35–70 times more likely to develop Crohnʼs disease than the general population. The crude risk of siblings or parents of patients with Crohnʼs disease developing ulcerative colitis may be half that of developing Crohnʼs disease; their relative risk may be a quarter that of developing Crohnʼs disease.