Intrahepatic cholestasis of pregnancy (ICP) is a liver disorder associated with increased risk of intrauterine fetal death and prematurity. There is increasing evidence that genetically determined dysfunction in the canalicular ABC transporters bile salt export pump (BSEP, ABCB11) and multidrug resistance protein 3 (MDR3, ABCB4) might be risk factors for ICP development. This study aimed to (i) describe the extent of genetic variability in BSEP and MDR3 in ICP and (ii) identify new disease-causing mutations. Twenty-one women with ICP and 40 women with uneventful pregnancies were recruited between April 2001 and April 2003. Sequencing of BSEP and MDR3 spanned 8–10 kb per gene and comprised the promoter region and 100–350 bp of the flanking intronic region around each exon. DNA sequencing of polymerase chain reaction fragments was performed on an ABI3700 capillary sequencer. MDR3 promoter activity of promoter constructs carrying different ICP-specific mutations was studied using reporter assays. A total of 37 and 51 variant sites were detected in BSEP and MDR3, respectively. Three non-synonymous sites in codons for evolutionarily conserved amino acids were specific for the ICP collective (BSEP, N591S; MDR3, S320F and G762E). Furthermore, four ICP-specific splicing mutations were detected in MDR3 [intron 21, G(+1)A; intron 25, G(+5)C and C(–3)G; and intron 26, T(+2)A]. Activity of the mutated MDR3 promoter was similar to that observed for the wild-type promoter. 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.
aDivision of Clinical Pharmacology and Toxicology and bDivision of Gastroenterology and Hepatology, Department of Internal Medicine, University Hospital Zürich, cDepartment of Gynaecology and Obstetrics, University Hospital Zürich, Zürich Switzerland, dDepartment of Medicine II, Klinikum Grosshadern, University of Munich, Munich, Germany, eDepartment of Medicine, University Hospital Bonn, Bonn, Germany and fEpidauros Biotechnology, Bernried, Germany.
Sponsorship: This work was supported by grants from the Gebert Rüf Foundation, the Forschungskredit of the University Zurich, the Swiss National Science Foundation (Grants 31-64140.00 and 632-062773) and the Bundesministerium für Bildung und Forschung (BMBF-01669848).
Correspondence and requests for reprints to Christiane Pauli-Magnus, University Hospital Zurich, Division of Clinical Pharmacology and Toxicology, Rämistrasse 100, 8091 Zurich, Switzerland. Tel: +41 1 255 4074; fax: +41 1 255 4411; e-mail: email@example.com
Received 14 August 2003 Accepted 14 November 2003