ATP-binding Cassette Transporter Defects and Their Roles in Hepatic Diseases

ATP-binding cassette (ABC) transporters are transmembrane proteins involved in the translocation of bilirubin, bile acids, phospholipids, and cholesterol into bile canaliculi. Mutations in particular genes encoding these transporters-including BSEP (<i>ABCB11</i> gene), MDR3 (<i>ABCB4</i> gene), sterolin-1 and sterolin-2 (<i>ABCG5/8</i> genes), and MRP2 (<i>ABCC2</i> gene)-result in a wide spectrum of liver diseases, ranging from benign conditions such as Dubin-Johnson syndrome to more severe presentations like progressive familial intrahepatic cholestasis. The severity of disease is influenced by many factors, including zygosity, mutation type, and environmental modifiers such as hormones, consanguinity, and founder effects. Homozygous and compound heterozygous mutations typically result in severe and early-onset diseases, while heterozygous single-allelic mutants generally result in milder diseases. Next-generation genetic testing has proven to have high diagnostic value and is important for prognostication. With knowledge of the underlying specific mutations, there is also potential for future targeted therapy for many severe diseases. The aim of this review is to update and discuss the hepatic diseases associated with ABC transporter mutations, the genetic and environmental effects that influence the severity of disease, typical presentations of these cholestatic hepatic diseases, diagnostic considerations, and treatment options.