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Progressive familial intrahepatic cholestasis (PFIC) is the name given to a group of genetic disorders that affect the liver. They result in the flow of bile from the liver to the gastrointestinal tract being reduced or stopping completely. This causes bile to accumulate in the liver cells (cholestasis), which start to die and are replaced with scar tissue. This leads to cirrhosis (severe scarring) and liver failure. PFIC is caused by mutations in the genes that encode the proteins involved in transporting bile out of the liver, adversely affecting their function. Three main types have been identified. The most prevalent, PFIC2, is caused by mutations in the ABCB11 gene. PFIC1 is caused by mutations in the ATP8B1 gene, and PFIC3 by mutations in the ABCB4 gene. Rarer types, such as PFIC4, PFIC5 and PFIC6, have been identified. PFIC is typically inherited in an autosomal recessive pattern, meaning that 2 copies of the mutated gene (1 from each parent) must be present for it to develop. In PFIC1 and PFIC2, symptoms usually occur in the first months of life. PFIC3 can also appear later in infancy, in childhood or even during young adulthood. PFIC progresses at varying rates dependent on the type, but usually develops into cirrhosis within the first decade of life. It is fatal if untreated.