ABCB4 gene mutations and single-nucleotide polymorphisms in women with intrahepatic cholestasis of pregnancy.
ABSTRACT To evaluate the nature and frequency of ATP-binding cassette subfamily B member 4 (ABCB4) gene variants in a series of French patients with intrahepatic cholestasis of pregnancy (ICP).
In this prospective study, the entire ABCB4 gene coding sequence was analysed by DNA sequencing in 50 unrelated women with ICP defined by pruritus and raised serum alanine aminotransferase activity or bile acid concentration, with recovery after delivery. Genomic variants detected in patients with ICP were sought in 107 control pregnant women. Patients with ICP and controls were of Caucasian origin.
Eight genomic variants were observed. One nonsense mutation (p.Arg144Stop) and two missense mutations (p.Ser320Phe and p.Thr775Met) were revealed each in one heterozygous patient. A third missense mutation (p.Arg590Gln) was detected in three heterozygous patients and in two homozygous patients also homozygous for a particular haplotype of three single-nucleotide polymorphisms (c.175C>T, c.504T>C, c.711A>T). The chromosomal frequency of the p.Arg590Gln variant was significantly different between the ICP and control group (7.0% vs 0.5%; p = 0.0017; OR 16.03, 95% CI 1.94 to 132.16). An association was also found between allele T of the c.504T>C silent nucleotide polymorphism and ICP (68.0% vs 53.7%; p = 0.017; OR 1.83, 95% CI 1.08 to 3.11). The chromosomal frequency of the p.Arg652Gly variant did not differ between the ICP and control group (p = 0.40).
This study shows that 16% of Caucasian patients with ICP bear ABCB4 gene mutations, and confirms the significant involvement of this gene in the pathogenesis of this complex disorder.
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ABSTRACT: Because ATP-binding cassette (ABC) transporters are important for normal bile secretion, hereditary and acquired ABC transporter defects play a central role in the pathogenesis of cholestasis. Defects of the phospholipid export pump MDR3 ( ABCC4) result in impaired biliary excretion of phosphatidylcholine and a variety of cholestatic syndromes ranging from progressive familial intrahepatic cholestasis in neonates to biliary cirrhosis in adults. Moreover, MDR3 mutations predispose to cholestasis of pregnancy and drug-induced cholestasis. Because MDR2 (rodent orthologue of human MDR3) knockout mice develop sclerosing cholangitis, it is attractive to speculate that MDR3 defects could also play an important role in cholangiopathies in humans. Indeed, MDR3 variants could play a role as modifier gene in primary biliary cirrhosis and primary sclerosing cholangitis, but their exact role needs further clarification. Impaired biliary phosphatidylcholine excretion has also been reported in total parenteral nutrition-induced cholestasis and bile duct injury following liver transplantation, but a genetic basis for these findings remains to be explored. Several drugs for the treatment of cholestatic liver diseases target MDR3 expression and function, further underscoring the clinical significance of this transport system.Seminars in Liver Disease 03/2007; 27(1):77-98. · 8.27 Impact Factor
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ABSTRACT: 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.Pharmacogenetics and Genomics 01/2004; 14(2):91-102. · 3.61 Impact Factor
- Journal of Medical Genetics 06/2003; 40(5):e70. · 5.70 Impact Factor