I've never heard it referred to as "fatal" (since many people never need a liver transplant, a liver transplant is an effective long-term treatment, and there are ways to slow down the progression and manage symptoms), but it's certainly serious.
More info on PSC (from
www.gicare.com/Diseases/Primary-Sclerosing-Cholangitis.aspx ):
"What is Primary Sclerosing Cholangitis (PSC)?
Primary sclerosing cholangitis is a disease primarily of the bile ducts, both inside and outside the liver. The ducts of the gallbladder and pancreas may also be involved. The walls of the bile ducts become inflamed (cholangitis). The inflammation causes scarring and hardening (fibrosis) that narrows the bile ducts. Because bile cannot drain properly through the ducts, it accumulates in the liver causing damage to liver cells. Eventually, so much bile is accumulated, it seeps into the bloodstream. Finally, with long term cell damage, the liver develops cirrhosis (hardening or fibrosis) and it can no longer function properly.
Cause
The exact cause of PSC is unknown. However, the most likely cause appears to be changes in the way the immune system works. When the immune system is working properly, it protects the body from infections caused by foreign invaders like bacteria and viruses. Sometimes, however, it recognizes certain body parts or organs as foreign. The body then goes to war against itself, damaging the body part it thinks is foreign.
PSC often starts between the ages of 30 and 50, and it occurs most often in men. It was once considered a rare disease, but recent studies show it is more common than previously thought. about
70% of the patients with PSC also have an inflammatory bowel disease, especially ulcerative colitis in which the colon becomes inflamed and ulcerated. Medical experts believe genetic factors may link PSC and ulcerative colitis."