Ulcerative colitis is one of the diseases that falls into the broader category of Irritable Bowel Disease (IBD). It's an inflammation of the colon (another name for the large intestine) and is closely related to another IBD, Crohn's disease. In fact, without proper testing it can be difficult for doctors to distinguish Crohn's from ulcerative colitis. This form of colitis can affect only the rectum, specific parts of the colon, or the entire colon.
In anywhere from 12 to 15 percent of cases, genetics seems to play a role in causing ulcerative colitis. Particularly at risk are people with a family history and also Ashkenazi Jews (Jews from middle or Eastern Europe).