Review article: liver disease in adults with variants in the cholestasis‐related genes <i>ABCB11</i>, <i>ABCB4</i> and <i>ATP8B1</i>
Jeremy Nayagam, Catherine Williamson, Deepak Joshi, Richard J. Thompson
Abstract
BACKGROUND: Children with intrahepatic cholestasis and genetic variants which result in the disruption of the formation and maintenance of bile (ABCB11, ABCB4 and ATP8B1) generally have a rapidly progressive clinical course. Adults with different phenotypes of cholestasis are increasingly being evaluated for variants in these genes associated with childhood diseases. AIMS: To review the literature with respect to the presence of variants in cholestasis-related genes in adults with various liver phenotypes, and provide clinical implications of the findings. METHODS: A search of the literature on variants in specific cholestasis-related genes in adults was conducted. RESULTS: The common variant p.Val444Ala in ABCB11 confers increased risk of drug-induced liver injury and intrahepatic cholestasis of pregnancy (ICP). Individuals with variants in ABCB4 are at risk of ICP and low phospholipid-associated cholelithiasis. Variants in ABCB4, and possibly ABCB11 and ATP8B1, can be identified in up to a third of patients with cryptogenic chronic cholestasis. CONCLUSIONS: Individuals with variants in ABCB11 rarely develop cholestasis until BSEP function dips below a threshold, which is also affected by other factors (e.g., drugs, hormones). However, variants in ABCB4 and consequent reduction in MDR3 protein, have a more linear dose-response curve. In individuals with an ABCB11 variant, medications known to reduce BSEP activity should be used cautiously; they should be monitored during pregnancy for ICP; and first-degree relatives should be counselled and screened. No proven management strategy exists, although ursodeoxycholic acid may be beneficial. Further work is needed to define the genotype-phenotype correlation and natural history, and to evaluate the penetrance.