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Contribution of variant alleles of ABCB11 to susceptibility to intrahepatic cholestasis of pregnancy
  1. P H Dixon1,
  2. S W C van Mil1,2,
  3. J Chambers1,
  4. S Strautnieks3,
  5. R J Thompson3,
  6. F Lammert4,
  7. R Kubitz5,
  8. V Keitel5,
  9. A Glantz6,
  10. L-Å Mattsson6,
  11. H-U Marschall7,
  12. M Molokhia8,
  13. G E Moore9,
  14. K J Linton10,
  15. C Williamson1
  1. 1
    Maternal and Fetal Disease Group, Institute of Reproductive and Developmental Biology, Imperial College London, London, UK
  2. 2
    Laboratory for Metabolic and Endocrine Diseases, UMC Utrecht, Utrecht, The Netherlands
  3. 3
    Department of Liver Studies and Transplantation, King’s College London School of Medicine, London, UK
  4. 4
    Department of Medicine I, Saarland University Hospital, Homburg, Germany
  5. 5
    Department of Gastroenterology, Hepatology and Infectious Diseases, University of Düsseldorf, Düsseldorf, Germany
  6. 6
    Department of Obstetrics and Gynecology, Sahlgrenska University Hospital/East, Göteborg, Sweden
  7. 7
    Karolinska Institutet, Department of Medicine at Karolinska University Hospital Huddinge, Stockholm, Sweden
  8. 8
    London School of Hygiene and Tropical Medicine, University of London, London, UK
  9. 9
    Institute of Child Health, University College London, London, UK
  10. 10
    MRC Clinical Sciences Centre, Imperial College London, London, UK
  1. Professor C Williamson, Maternal and Fetal Disease Group, Institute of Reproductive and Developmental Biology, Division of Surgery, Oncology, Reproductive Biology and Anaesthetics, Faculty of Medicine, Imperial College London, Hammersmith Campus, Du Cane Road, London W12 0NN, UK; catherine.williamson{at}imperial.ac.uk

Abstract

Background: Intrahepatic cholestasis of pregnancy (ICP) has a complex aetiology with a significant genetic component. ABCB11 encodes the bile salt export pump (BSEP); mutations cause a spectrum of cholestatic disease, and are implicated in the aetiology of ICP.

Methods: ABCB11 variation in ICP was investigated by screening for five mutant alleles (E297G, D482G, N591S, D676Y and G855R) and the V444A polymorphism (c.1331T>C, rs2287622) in two ICP cohorts (n = 333 UK, n = 158 continental Europe), and controls (n = 261) for V444A. PCR primers were used to amplify and sequence patient and control DNA. The molecular basis for the observed phenotypes was investigated in silico by analysing the equivalent residues in the structure of the homologous bacterial transporter Sav1866.

Results: E297G was observed four times and D482G once. N591S was present in two patients; D676Y and G855R were not observed. The V444A polymorphism was associated with ICP (allelic analysis for C vs T: OR 1.7 (95% CI 1.4 to 2.1, p<0.001)). In addition, CC homozygotes were more likely to have ICP than TT homozygotes: OR 2.8 (95% CI 1.7 to 4.4 p<0.0001). Structural analyses suggest that E297G and D482G destabilise the protein fold of BSEP. The molecular basis of V444A and N591S was not apparent from the Sav1866 structure.

Conclusions: Heterozygosity for the common ABCB11 mutations accounts for 1% of European ICP cases; these two mutants probably reduce the folding efficiency of BSEP. N591S is a recurrent mutation; however, the mechanism may be independent of protein stability or function. The V444A polymorphism is a significant risk factor for ICP in this population.

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Footnotes

  • Competing interests: None.

  • Funding: Our research is supported by Wellbeing of Women, the Lauren Page Trust, the Institute of Obstetrics and Gynaecology Trust, the Biomedical Research Centre at Imperial College Healthcare NHS Trust, the German Research Council, the Department of Research and Development (FoU), Västra Götaland, Sweden, the Guy’s and St Thomas Charity London UK and the Children’s liver disease foundation, Birmingham, UK.

  • Ethics approval: Permission for this study was obtained from the Ethics Committees of the Hammersmith Hospitals NHS Trust, London (REC 97/5197), the Ethics Committee of the Faculty of Medicine at the University of Göteborg and the University Hospital Aachen, Germany

  • ▸ An additional figure is published online only at http://gut.bmj.com/content/vol58/issue4

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