title: Heterozygous MDR3 missense mutation associated with intrahepatic cholestasis of pregnancy: evidence for a defect in protein trafficking.
abstract: Intrahepatic cholestasis of pregnancy (ICP) is a liver disease of pregnancy with serious consequences for the mother and fetus. Two pedigrees have been reported with ICP in the mothers of children with a subtype of autosomal recessive progressive familial intrahepatic cholestasis (PFIC) with raised serum gamma-glutamyl transpeptidase (gamma-GT). Affected children have homozygous mutations in the MDR3 gene (also called ABCB4 ), and heterozygous mothers have ICP. More frequently, however, ICP occurs in women with no known family history of PFIC and the genetic basis of this disorder is unknown. We investigated eight women with ICP and raised serum gamma-GT, but with no known family history of PFIC. DNA sequence analysis revealed a C to A transversion in codon 546 in exon 14 of MDR3 in one patient, which results in the missense substitution of the wild-type alanine with an aspartic acid. We performed functional studies of this mutation introduced into MDR1, a closely related homologue of MDR3. Fluorescence activated cell sorting (FACS) and western analysis indicated that this missense mutation causes disruption of protein trafficking with a subsequent lack of functional protein at the cell surface. The demonstration of a heterozygous missense mutation in the MDR3 gene in a patient with ICP with no known family history of PFIC, analysed by functional studies, is a novel finding. This shows that MDR3 mutations are responsible for the additional phenotype of ICP in a subgroup of women with raised gamma-GT.
authors.affiliation: Division of Medicine, Imperial College School of Medicine, London, UK.
authors.forename: P H
authors.initials: PH
authors.lastname: Dixon
authors.forename: N
authors.initials: N
authors.lastname: Weerasekera
authors.forename: K J
authors.initials: KJ
authors.lastname: Linton
authors.forename: O
authors.initials: O
authors.lastname: Donaldson
authors.forename: J
authors.initials: J
authors.lastname: Chambers
authors.forename: E
authors.initials: E
authors.lastname: Egginton
authors.forename: J
authors.initials: J
authors.lastname: Weaver
authors.forename: C
authors.initials: C
authors.lastname: Nelson-Piercy
authors.forename: M
authors.initials: M
authors.lastname: de Swiet
authors.forename: G
authors.initials: G
authors.lastname: Warnes
authors.forename: E
authors.initials: E
authors.lastname: Elias
authors.forename: C F
authors.initials: CF
authors.lastname: Higgins
authors.forename: D G
authors.initials: DG
authors.lastname: Johnston
authors.forename: M I
authors.initials: MI
authors.lastname: McCarthy
authors.forename: C
authors.initials: C
authors.lastname: Williamson
mesh_terms: D018435:ATP Binding Cassette Transporter, Subfamily B / Q000235:genetics*; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics; D018528:ATP-Binding Cassette Transporters / Q000235:genetics*; D019943:Amino Acid Substitution; D002460:Cell Line; D002648:Child; D002780:Cholestasis, Intrahepatic / Q000235:genetics*; D003062:Codon; D005091:Exons; D005260:Female; D005808:Genes, Recessive; D006579:Heterozygote; D006801:Humans; D007231:Infant, Newborn; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D020125:Mutation, Missense; D011247:Pregnancy; D011248:Pregnancy Complications; D017433:Protein Structure, Secondary; D014162:Transfection; D005723:gamma-Glutamyltransferase / Q000097:blood
chemical_list: D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D018528:ATP-Binding Cassette Transporters; D003062:Codon; C095122:multidrug resistance protein 3; D005723:gamma-Glutamyltransferase