Contrasting impacts of two ABCB11 variants affecting the same residue in progressive familial intrahepatic...

Progressive familial intrahepatic cholestasis type 2 (PFIC2) is a severe autosomal recessive cholestatic liver disease due to variations in ATP-binding cassette subfamily B member 11 (ABCB11) gene. The clinical and molecular consequences of two missense variations affecting the same ABCB11 residue (T463) were characterized, and pharmacological strategies were investigated. Clinical and genetic data were collected from two PFIC2 patients carrying p.T463I or p.T463P substitutions. A three-dimensional (3-D) structure analysis was performed to predict substitution impacts. ABCB11^T463I and ABCB11^T463P variants were expressed in HepG2 and Madin-Darby canine kidney cells to assess their subcellular localization and functional activity. Pharmacological modulators were tested to correct the defects. The patient carrying ABCB11^T463I exhibited a mild phenotype and responded to surgical biliary diversion. Conversely, the patient carrying ABCB11^T463P required a liver transplantation before age one. 3-D structure and in vitro analyses predicted a functional defect in both variants and a folding defect for the T463P variant. In vitro, ursodeoxycholic acid combined with glycerol phenylbutyrate increased ABCB11^T463P canalicular expression (40.2 ± 7.7% of the wild type, P < 0.0001) and improved transport activity (32.4 ± 10.3% of the wild type, P < 0.0001). VX-770 and SBC040 increased ABCB11^T463I function from 37.9 ± 2.5% (DMSO) to 73.2 ± 12.3% and 76.1 ± 17.5%, respectively, of the wild-type activity (P < 0.0001). ABCB11 missense variations, even affecting the same residue, can cause various molecular defects, resulting in mild to severe phenotypes. 3-D structure and in vitro analyses could be used to predict the severity of missense variants and guide the treatment of PFIC2 patients with pharmacological modulators.NEW & NOTEWORTHY Patients with progressive familial intrahepatic cholestasis type 2 (PFIC2) due to ATP-binding cassette subfamily B member 11 (ABCB11) missense variations may present various phenotypes and exhibit different response patterns to treatments. This study exemplifies this variability and provides an in silico and in vitro framework for characterizing and classifying ABCB11 missense variants. This classification could serve to guide treatment strategies, stratify patients with missense variants in clinical trials, and predict patient outcomes.