Mutational analysis of ABCB4 in patients and their families should be considered in all individuals with cholestasis of unknown aetiology, regardless of age and/or time of onset of the first symptoms.
Bland canalicular cholestasis is the prototypic change but it is now clear that some gene mutations, particularly in ABCB4 (encoding MDR3), can cause other patterns that include early cholesterol calculus formation, bile duct injury and disappearance, ductular reactions mimicking large duct obstruction and, in rare cases, progressive fibrosis.
Sequencing of genes encoding for hepatic transporters for bile acid homeostasis (BSEP, MDR3, and FIC1) found no genetic variants typically associated with hereditary cholestasis syndromes.
Thirty-three patients with unexplained cholestasis despite a thorough clinical work-up were examined for sequence variations in the coding regions of the ABCB4, ABCB11, ABCC2, ABCG5, ATP8B1, JAG1, NOTCH2, and UGT1A1 genes and the promoter region of UGT1A1 by massive parallel sequencing of DNA extracted from whole blood.
Correlation between GNMT and miR-873-5p in human cholestasis and cirrhosis together with miR-873-5p inhibition in vivo in different mouse models of liver cholestasis and fibrosis [bile duct ligation and Mdr2 (Abcb4)<sup>-/-</sup> mouse] were then assessed.
To elucidate the mechanisms of bile acid-induced liver injury, we assessed signs of liver damage and gene expression in Abcb4-/- mice, a well-known model for cholestasis.
Bcl3(-/-)Mdr2(-/-) mice developed more severe cholestasis and had increased markers of liver injury and increased proliferation of biliary epithelial cells and hepatocytes than Mdr2(-/-) mice.
ABCB4(S320F) homozygosity, with half the normal level of ABCB4, is the tipping point between more benign and potentially fatal cholestasis and makes these patients more acutely sensitive to environmental effects.
Between February 2004 and March 2007, all adults with unexplained cholestasis despite multiple investigations including liver biopsy and 124 healthy volunteers had ABCB4 sequencing.
Defect in ABCB4 function causes the production of bile with low phospholipid content, increased lithogenicity and high detergent properties leading to bile duct luminal membrane injuries and resulting in cholestasis with increased serum gamma-glutamyltransferase (GGT) activity.
Our data further support an involvement of MDR3 genetic variation in the pathogenesis of ICP, whereas analysis of BSEP sequence variation indicates that this gene is probably less important for the development of pregnancy-associated cholestasis.
Those patients presenting high GGT-PFIC with early onset cholestasis but without MDR3 mutation probably had inheritable disorders remaining to be clarified.