Molecular overview of progressive familial intrahepatic cholestasis

Abstract

Cholestasis is a clinical condition resulting from the imapairment of bile flow. This condition could be caused by defects of the hepatocytes, which are responsible for the complex process of bile formation and secretion, and/or caused by defects in the secretory machinery of cholangiocytes. Several mutations and pathways that lead to cholestasis have been described. Progressive familial intrahepatic cholestasis (PFIC) is a group of rare diseases caused by autosomal recessive mutations in the genes that encode proteins expressed mainly in the apical membrane of the hepatocytes. PFIC 1, also known as Byler’s disease, is caused by mutations of the ATP8B1 gene, which encodes the familial intrahepatic cholestasis 1 protein. PFIC 2 is characterized by the downregulation or absence of functional bile salt export pump (BSEP) expression via variations in the ABCB11 gene. Mutations of the ABCB4 gene result in lower expression of the multidrug resistance class 3 glycoprotein, leading to the third type of PFIC. Newer variations of this disease have been described. Loss of function of the tight junction protein 2 protein results in PFIC 4, while mutations of the NR1H4 gene, which encodes farnesoid X receptor, an important transcription factor for bile formation, cause PFIC 5. A recently described type of PFIC is associated with a mutation in the MYO5B gene, important for the trafficking of BSEP and hepatocyte membrane polarization. In this review, we provide a brief overview of the molecular mechanisms and clinical features associated with each type of PFIC based on peer reviewed journals published between 1993 and 2020.

Keywords: Progressive familial intrahepatic cholestasis, ATP8B1/familial intrahepatic cholestasis 1, ABCB11/bile salt export pump, ABCB4/multidrug resistance class 3, Intrahepatic cholestasis, Bile

Core Tip: Progressive familial intrahepatic cholestasis (PFIC) is an expanding group of genetically-based diseases caused by various autosomal recessive mutations which result in the inability to appropriately form and excrete bile from hepatocytes. There are three classic types of PFIC. Type 1 is caused by mutations of the ATP8B1 gene, encoding familial intrahepatic cholestasis 1. PFIC 2 is the result of mutations in the ABCB11 gene, reducing the apical membrane expression of bile salt export pump. PFIC 3 is caused by variations in the gene that encodes the multidrug resistance class 3 glycoprotein. With advances in DNA sequencing, new forms of this disease have been documented. Alterations in the NR1H4, tight junction protein 2, and MYO5B genes have been linked with new phenotypes of PFIC. Here, we provide a molecular and clinical overview of PFIC.