Primary Biliary Cirrhosis - Etiology

Etiology

The cause of the disease is unknown at this time, but research indicates that there is an immunological basis for the disease, making it an autoimmune disorder. Most of the patients (>90%) seem to have anti-mitochondrial antibodies (AMAs) against pyruvate dehydrogenase complex (PDC-E2), an enzyme complex that is found in the mitochondria.

Primary biliary cirrhosis is considerably more common in those with gluten sensitive enteropathy than the normal population. In some cases of disease protein expression may cause an immune tolerance failure, as might be the case with gp210 and p62, nuclear pore proteins. Gp210 has increased expression in the bile duct of anti-gp210 positive patients. Both proteins appear to be prognostic of liver failure relative to anti-mitochondrial antibodies.

A genetic predisposition to disease has been thought important for some time, as evident by cases of PBC in family members, concordance in identical twins, and clustering of autoimmune diseases. In 2009 a Canadian led group of investigators reported in the New England Journal of Medicine results from the first PBC genome-wide association study. This research revealed parts of the IL12 signaling cascade, particularly IL12A and IL12RB2 polymorphisms, to be important in the etiology of the disease in addition to the HLA region. In 2012, two independent PBC association studies increased the total number of genomic regions associated to 26, implicating many genes involved in cytokine regulation such as TYK2, SH2B3 and TNFSF11.

In 2003 it was reported that an environmental Gram negative alphabacterium — Novosphingobium aromaticivorans was strongly associated with this disease. Subsequent reports appear to have confirmed this finding suggesting an aetiological role for this organism. The mechanism appears to be a cross reaction between the proteins of the bacterium and the mitochondrial proteins of the liver cells. The gene encoding CD101 may also play a role in host susceptibility to this disease.