Molecular overview of progressive familial intrahepatic cholestasis

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.

Expanding etiology of progressive familial intrahepatic cholestasis

BACKGROUND Progressive familial intrahepatic cholestasis(PFIC)refers to a disparate group of autosomal recessive disorders that are linked by the inability to appropriately form and excrete bile from hepatocytes,resulting in a hepatocellular form of cholestasis.While the diagnosis of such disorders had historically been based on pattern recognition of unremitting cholestasis without other identified molecular or anatomic cause,recent scientific advancements have uncovered multiple specific responsible proteins.The variety of identified defects has resulted in an ever-broadening phenotypic spectrum,ranging from traditional benign recurrent jaundice to progressive cholestasis and end-stage liver disease.AIM To review current data on defects in bile acid homeostasis,explore the expanding knowledge base of genetic based diseases in this field,and report disease characteristics and management.METHODS We conducted a systemic review according to PRISMA guidelines.We performed a Medline/PubMed search in February-March 2019 for relevant articles relating to the understanding,diagnosis,and management of bile acid homeostasis with a focus on the family of diseases collectively known as PFIC.English only articles were accessed in full.The manual search included references of retrieved articles.We extracted data on disease characteristics,associations with other diseases,and treatment.Data was summarized and presented in text,figure,and table format.RESULTS Genetic-based liver disease resulting in the inability to properly form and secrete bile constitute an important cause of morbidity and mortality in children and increasingly in adults.A growing number of PFIC have been described based on an expanded understanding of biliary transport mechanism defects and the development of a common phenotype.CONCLUSION We present a summary of current advances made in a number of areas relevant to both the classically described FIC1(ATP8B1),BSEP(ABCB11),and MDR3(ABCB4)transporter deficiencies,as well as more recently described gene mutations--TJP2(TJP2),FXR(NR1H4),MYO5B(MYO5B),and others which expand the etiology and understanding of PFIC-related cholestatic diseases and bile transport.