ABSTRACT
BACKGROUND & AIMS: 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.
Subject(s)
ATP Binding Cassette Transporter, Subfamily B/deficiency , Cholestasis, Intrahepatic , Liver Cirrhosis, Biliary , ATP Binding Cassette Transporter, Subfamily B/genetics , Adolescent , Child , Child, Preschool , Cholestasis, Intrahepatic/complications , Cholestasis, Intrahepatic/diagnosis , Cholestasis, Intrahepatic/genetics , Codon, Nonsense , Female , Genetic Predisposition to Disease , Heterozygote , Humans , Infant , Liver Cirrhosis, Biliary/etiology , Liver Cirrhosis, Biliary/genetics , Liver Cirrhosis, Biliary/physiopathology , Male , Mutation, MissenseABSTRACT
Pediatric acute liver failure is a syndrome ofsevere and sudden dysfunction of the hepatocytes which produces a failure in synthetic and detoxifyingfunction. It is an infrequent and severe disease butpotentiallyfatal, occurring in children with no prior history of liver disease. Etiology is related to the age and geographic region of the patient, recognizing the origin: metabolic, infectious, drug exposure, autoinmune, vascular and oncologic. Indeterminate cause where all the etiological search is negative, can range between 18 and 47%, depending on the center and access to the realization of etiological studies. The process which determines the liver injury is still not well known and is considered multifactorial. Essentially, it depends on host susceptibility, the cause and severity of the damage and the ability of liver regeneration. The clinical presentation depends on the etiology, which usually begins with an episode ofacute hepatitis, that in the following days or weeks presents unfavorable outcome, deepening jaundice, affecting the general state and presenting severe coagulopathy that characterizes the syndrome. The treatment consists of general measures which take into account the metabolic disorders, nutritional aspect, and the prevention and treatment of all complications that occur in the evolutionary course (infectious, neurological, etc). Besides it is also vital to implement the specific treatment of those diseases which can benefit from it (alloimmune hepatitis, galactosemia, tyrosinemia, herpes simplex infection, Wilson's disease, etc.). However, despite therapeutic advances, acute liver failure results in death or liver transplantation in over 45% ofcases.
