Intrahepatic cholestasis of pregnancy: molecular pathogenesis, diagnosis and management

Hereditary forms of intrahepatic cholestasis

Several genes that are mutated in hereditary forms of intrahepatic cholestasis have been identified or mapped, providing new insights into the process of enterohepatic bile acid circulation in health and disease and new tools with which to study this process. Murine models of several of these disorders have been generated. Unanticipated genetic heterogeneity has been identified.

Inherited metabolic diseases of the liver

Many inherited metabolic diseases affect the liver in neonates, children, or adults. The histopathologic changes are diverse and may be acute or chronic. They can be considered primary (when the injury is from the cytopathic effect of an accumulated metabolite) or secondary (e.g., an infection caused by an immune deficiency). All forms of liver disease are described: for example, intrahepatic cholestasis, neonatal hepatitis with giant-cell transformation, paucity of bile ducts, steatosis, steatohepatitis, necroinflammatory diseases (acute or chronic), fibrosis, cirrhosis, and neoplasms (benign or malignant). Familiarity with the morphologic changes is important in clinicopathologic correlation, diagnosis, and understanding of pathogenetic mechanisms.

Genetic defects in hepatobiliary transport

Bile formation, the exocrine function of the liver, represents a process that is unique to the hepatocyte as a polarized epithelial cell. The generation of bile flow is an osmotic process and largely depends on solute secretion by primary active transporters in the apical membrane of the hepatocyte. In recent years an impressive progress has been made in the discovery of these proteins, most of which belong to the family of ABC transporters. The number of identified ABC transporter genes has been exponentially increasing and the mammalian subfamily now counts at least 52. This development has been of crucial importance for the elucidation of the mechanism of bile formation, and it is therefore not surprising that the development in this field has run in parallel with the discovery of the ABC genes. With the identification of these transporter genes, the background of a number of inherited diseases, which are caused by mutations in these solute pumps, has now been elucidated. We now know that at least six primary active transporters are involved in canalicular secretion of biliary components (MDR1, MDR3, BSEP, MRP2, BCRP and FIC1). Four of these transporter genes are associated with inherited diseases. In this minireview we will shortly describe our present understanding of bile formation and the associated inherited defects.

Cholestatic syndromes

New insights into the regulation of hepatobiliary transport proteins have provided the basis for a better understanding of the pathogenesis of cholestatic liver diseases. Mutations of transporter genes can cause hereditary cholestatic syndromes, the study of which has shed much light on the basic mechanisms of bile secretion and cholestasis. Important new studies have been published about the pathogenesis, clinical features, and treatment of primary biliary cirrhosis, primary sclerosing cholangitis, cholestasis of pregnancy, total parenteral nutrition-induced cholestasis, and drug-induced cholestasis.