title: Heterozygous ABCB4 mutations in children with cholestatic liver disease.
abstract: OBJECTIVE
  Monoallelic defects in ABCB4, which encodes the canalicular floppase for phosphatidylcholine MDR3, have been encountered in association with a variety of hepatobiliary disorders, particularly in adult subjects. In this study, we examined the presence of heterozygous ABCB4 variants in a cohort of children with chronic cholestasis and assessed the pathogenicity of the missense changes identified.
  
  
  METHODS
  Sixty-seven children with chronic liver dysfunction were studied by the sequencing of ABCB4 and multiplex ligation-dependent probe amplification analysis. The molecular defects arising from missense variants were analysed in MDCK-II and AD-293 cells.
  
  
  RESULTS
  Defects in a single allele of ABCB4 were identified in nine subjects. They included one small insertion (p.I1242Nfs), one nonsense mutation (p.R144X) and six missense changes (p.T175A, p.G228R, p.A250T, p.S320F, p.P352L and p.A934T). In four children, these defects in ABCB4 co-existed with various medical conditions. In vitro phenotyping of the six missense variants revealed that four (T175A, G228R, S320F and A934T) led to reduced MDR3 protein levels. Two mutations (G228R and A934T) resulted in trapping of the protein in the endoplasmic reticulum. Phosphatidylcholine efflux activity was decreased to 56-18% of reference levels for MDR3 mutants T175A, A250T and S320F. The G228R, P352L and A934T mutants were found to be non-functional.
  
  
  CONCLUSIONS
  These results illustrate the varying effects of ABCB4 missense mutations and suggest that even a modest reduction in MDR3 activity may contribute or predispose to the onset of cholestatic liver disease in the paediatric age.
authors.affiliation: La Paz University Hospital Health Research Institute-IdiPAZ, Madrid, Spain.
authors.forename: Raquel
authors.initials: R
authors.lastname: Gordo-Gilart
authors.affiliation: La Paz University Hospital Health Research Institute-IdiPAZ, Madrid, Spain.|Pediatric Liver Service, La Paz Children's University Hospital, Madrid, Spain.
authors.forename: Loreto
authors.initials: L
authors.lastname: Hierro
authors.affiliation: La Paz University Hospital Health Research Institute-IdiPAZ, Madrid, Spain.
authors.forename: Sara
authors.initials: S
authors.lastname: Andueza
authors.affiliation: La Paz University Hospital Health Research Institute-IdiPAZ, Madrid, Spain.|Pediatric Liver Service, La Paz Children's University Hospital, Madrid, Spain.
authors.forename: Gema
authors.initials: G
authors.lastname: Muñoz-Bartolo
authors.affiliation: Pediatric Gastroenterology, Hepatology and Nutrition Unit, Pereira Rossell Hospital, Montevideo, Uruguay.
authors.forename: Carola
authors.initials: C
authors.lastname: López
authors.affiliation: La Paz University Hospital Health Research Institute-IdiPAZ, Madrid, Spain.|Pediatric Liver Service, La Paz Children's University Hospital, Madrid, Spain.
authors.forename: Carmen
authors.initials: C
authors.lastname: Díaz
authors.affiliation: La Paz University Hospital Health Research Institute-IdiPAZ, Madrid, Spain.|Pediatric Liver Service, La Paz Children's University Hospital, Madrid, Spain.
authors.forename: Paloma
authors.initials: P
authors.lastname: Jara
authors.affiliation: La Paz University Hospital Health Research Institute-IdiPAZ, Madrid, Spain.
authors.forename: Luis
authors.initials: L
authors.lastname: Álvarez
mesh_terms: D018435:ATP Binding Cassette Transporter, Subfamily B / Q000172:deficiency* / Q000235:genetics; D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D002780:Cholestasis, Intrahepatic / Q000150:complications / Q000175:diagnosis / Q000235:genetics; D018389:Codon, Nonsense; D005260:Female; D020022:Genetic Predisposition to Disease; D006579:Heterozygote; D006801:Humans; D007223:Infant; D008105:Liver Cirrhosis, Biliary / Q000209:etiology / Q000235:genetics / Q000503:physiopathology; D008297:Male; D020125:Mutation, Missense
chemical_list: D018435:ATP Binding Cassette Transporter, Subfamily B; D018389:Codon, Nonsense; C095122:multidrug resistance protein 3
keywords: ABCB4; MDR3; PFIC3; cholestasis; gene mutation