Primary sclerosing cholangitis (PSC) is a long-term progressive disease of the liver and gallbladder characterized by inflammation and scarring of the bile ducts, which normally allow bile to drain from the gallbladder. Affected individuals may have no symptoms or may experience signs and symptoms of liver disease, such as yellow discoloration of the skin and eyes, itching, and abdominal pain. The bile duct scarring that occurs in PSC narrows the ducts of the biliary tree and impedes the flow of bile to the intestines. Eventually, it can lead to cirrhosis of the liver and liver failure. PSC increases the risk of various cancers, including liver cancer, gallbladder carcinoma, colorectal cancer, and cholangiocarcinoma. The underlying cause of PSC is unknown. Genetic susceptibility, immune system dysfunction, and abnormal composition of the gut flora may play a role. This is further suggested by the observation that around 75% of individuals with PSC also have inflammatory bowel disease (IBD), most often ulcerative colitis. No effective medical treatment for primary sclerosing cholangitis is known. Its most definitive treatment is a liver transplant, but it can recur after transplantation. Many people affected by PSC require a liver transplant. PSC is a rare disease and most commonly affects people with IBD. About 3.0 to 7.5% of people with ulcerative colitis have PSC, and 80% of people with PSC have some form of IBD. Diagnosis usually occurs in people in their 30s or 40s. Individuals of Northern European ancestry are affected more often than people of Southern European or Asian descent. Men are affected more often than women. The disease was initially described in the mid-1800s, but was not fully characterized until the 1970s with the advent of improved medical-imaging techniques such as endoscopic retrograde cholangiopancreatography. Signs and symptoms Nearly half of people with PSC do not have symptoms, and are often incidentally discovered to have PSC due to abnormal liver function tests; however, a substantial proportion have debilitating signs and symptoms of the disease. Signs and symptoms of PSC may include severe itching and nonspecific fatigue. Yellowing of the skin and white portion of the eyes may also be seen. Enlargement of the liver and spleen are seen in roughly 40% of affected individuals. Abdominal pain affects about 20% of people with PSC. Multiple episodes of life-threatening acute cholangitis (infection within the bile ducts) can be seen due to impaired drainage of the bile ducts, which increases