In Mdr2KO mice, the ablation of ABCB4 gene encoding for the multidrug resistance protein 2 (Mdr2), a membrane protein with flippase activity and a role in the hepato-canalicular transport of phospholipids, results in bile retention in the liver and cholestasis-induced hepatic fibrosis25–27. This evidence concerns the gene ABCB4 and cholestasis.