Novel ABCB11 mutations in a Thai infant with progressive familial intrahepatic cholestasis

Progressive familial intrahepatic cholestasis （PFIC） type 2 is caused by mutations in ABCB11, which encodes bile salt export pump （BSEP）. We report a Thai female infant who presented with progressive cholestatic jaundice since 1 mo of age, with normal serum y-glutamyltransferase. Immunohistochemical staining of the liver did not demonstrate BSEP along the canaliculi, while multidrug resistance protein 3 was expressed adequately. Novel mutations in ABCB11, a four-nucleotide deletion in exon 3, c.90_93delGAAA, and a single-nucleotide insertion in exon 5, c.249_250insT, were identified, with confirmation in her parents. These mutations were predicted to lead to synthesis of truncated forms of BSEP. Immunostaining and mutation analysis thus established the diagnosis of PFIC type     

Hepatocellular carcinoma in ten children under five years of age with bile salt export pump deficiency

Hepatocellular carcinoma (HCC) is rare in young children. We attempted to see if immunohistochemical and mutational-analysis studies could demonstrate that deficiency of the canalicular bile acid transporter bile salt export pump (BSEP) and mutation in ABCB11, encoding BSEP, underlay progressive familial intrahepatic cholestasis (PFIC)--or "neonatal hepatitis" suggesting PFIC--that was associated with HCC in young children. We studied 11 cases of pediatric HCC in the setting of PFIC or "neonatal hepatitis" suggesting PFIC. Archival liver were retrieved and immunostained for BSEP. Mutational analysis of ABCB11 was performed in leukocyte DNA from available patients and parents. Among the 11 nonrelated children studied aged 13-52 months at diagnosis of HCC, 9 (and a full sibling, with neonatal hepatitis suggesting PFIC, of a tenth from whom liver was not available) had immunohistochemical evidence of BSEP deficiency; the eleventh child did not. Mutations in ABCB11 were demonstrated in all patients with BSEP deficiency in whom leukocyte DNA could be studied (n = 7). These mutations were confirmed in the parents (n = 14). With respect to the other 3 children with BSEP deficiency, mutations in ABCB11 were demonstrated in all 5 parents in whom leukocyte DNA could be studied. Thirteen different mutations were found. In conclusion, PFIC associated with BSEP deficiency represents a previously unrecognized risk for HCC in young children. Immunohistochemical evidence of BSEP deficiency correlates well with demonstrable mutation in ABCB11.     

Impaired expression and function of the bile salt export pump due to three novel ABCB11 mutations in intrahepatic cholestasis

BACKGROUND/AIMS: Inherited dysfunction of the bile salt export pump BSEP (ABCB11) causes a progressive and a benign form of familial intrahepatic cholestasis, denominated as PFIC2 and BRIC2, respectively. We functionally characterized novel ABCB11 mutations encountered in two patients with a PFIC2 and a BRIC2 phenotype, respectively. METHODS: BSEP expression was determined in liver biopsies by immunohistochemistry. ABCB11 mutations were functionally characterized by taurocholate transport in SF9 cells transfected with human ABCB11. RESULTS: The PFIC2 patient was compound heterozygous for a splicing mutation in intron 4 ((+3)A > C) combined with an early stop codon at position 930 (R930X), while the BRIC2 patient was compound heterozygous for two nonsynonymous mutations in exon 9 (E297G) and exon 12 (R432T), respectively. Hepatic BSEP expression was absent in PFIC2 and preserved in BRIC2. In BRIC2, taurocholate transport was decreased to 13% and 20% of reference levels for R432T and E297G, respectively. CONCLUSIONS: The intron 4 (+3)A > C, R930X and R432T represent previously undescribed mutations of the ABCB11 gene that confer a PFIC2 and a BRIC2 phenotype, respectively. By combining functional in-vitro characterization with immunohistochemical detection of variant BSEP we provide direct evidence for the role of ABCB11 mutations in the pathogenesis of different forms of intrahepatic cholestasis.     

Benign recurrent intrahepatic cholestasis type 2 is caused by mutations in ABCB11

BACKGROUND & AIMS: Progressive familial intrahepatic cholestasis (PFIC) and benign recurrent intrahepatic cholestasis (BRIC) are hereditary liver disorders; PFIC is characterized by severe progressive liver disease whereas BRIC patients have intermittent attacks of cholestasis without permanent liver damage. Mutations in ATP8B1 are present in PFIC type 1 and in a subset of BRIC patients. We hypothesized that a genetically distinct form of BRIC is associated with mutations in ABCB11. This gene encodes the bile salt export pump (BSEP) and is mutated in PFIC type 2. METHODS: Patients from 20 families were included; all had a normal ATP8B1 sequence. Sequencing of all 27 coding exons including the splice junctions of ABCB11 revealed 8 distinct mutations in 11 patients from 8 different families: one homozygous missense mutation (E297G) previously described in PFIC2 patients, 6 novel missense mutations, and one putative splice site mutation. RESULTS: In 12 families, no mutations in ATB8B1 or ABCB11 were detected. Pancreatitis is a known extrahepatic symptom in BRIC caused by ATP8B1 mutations, but was not present in BRIC patients with mutations in ABCB11. In contrast, cholelithiasis was observed in 7 of 11 BRIC patients with mutations in ABCB11, but has not been described in ATP8B1-affected BRIC patients. CONCLUSIONS: Mutations in ABCB11 are associated with BRIC, and consistent with the genetic classification of PFIC into 2 subtypes, we propose that this disorder be named BRIC type 2.     

A study of exons 14, 15, and 24 of the ABCB11 gene in Egyptian children with normal GGT cholestasis

Background and study aimsProgressive familial intrahepatic cholestasis type 2 (PFIC2) is a rare inherited disorder caused by mutation in the ATP-binding cassette subfamily B member 11 gene (ABCB11) that encodes the bile salt export pump (BSEP), which is the main transporter of bile acids from hepatocytes to the canalicular lumen. Defects in BSEP synthesis and/or function lead to reduced bile salt secretion followed by accumulation of bile salts in hepatocytes and hepatocellular damage. This study aimed to detect variations in exons 14, 15, and 24 of the ABCB11 gene in patients with suspected PFIC2 among a group of Egyptian infants and children with normal gamma-glutamyl transpeptidase (GGT) cholestasis.Patients and methodsThis observational case-control study was conducted on 13 children with suspected PFIC2 and 13 healthy subjects as controls. Genotyping of the ABCB11 gene was performed via DNA extraction followed by PCR amplification, purification, and then sequencing analysis of exons 14, 15, and 24 of the ABCB11 gene.ResultsThe study detected two single nucleotide variations, c.1638+ 32T > C (rs2241340) in exon 14 and c.3084A > G (p.Ala1028 = ) (rs497692) in exon 24 of the ABCB11 gene. No variations were identified in exon 15.ConclusionThe study revealed two benign variants involving exons 14 and 24 of the ABCB11 gene. Exons 14, 15, and 24 are not hot spots for common mutations in Egyptian PFIC2 patients. Further study of other exons of the ABCB11 gene is necessary to confirm the diagnosis of PFIC2.     

Antisense oligonucleotides rescue an intronic splicing variant in the ABCB11 gene that causes progressive familial intrahepatic cholestasis type 2

BackgroundProgressive familial intrahepatic cholestasis type 2 (PFIC2) is a rare disorder caused by variants in the ABCB11 gene encoding the bile salt export pump (BSEP). We investigated the molecular defect in a PFIC2 infant and rescued the splicing defect with antisense oligonucleotides (ASOs).MethodsWhole-exome sequencing (WES) revealed compound heterozygous variants in the ABCB11 gene in a PFIC2 patient. Liver biopsy was immunostained for BSEP. The splicing effect of the candidate variants was investigated by minigene assay. ASOs were designed to rescue aberrant splicing.ResultsA Chinese girl of two nonconsanguineous healthy parents suffered from low glutamyl transpeptidase cholestasis and showed no response to the ursodeoxycholic acid. WES revealed that the patient was compound heterozygous for two novel variants in the ABCB11 gene: c.76+29T>G and c.390–2A>G. Liver immunohistochemistry showed the absence of BSEP. The variant c.76+29T>G was confirmed to retain 42 bp in the mature mRNA. The variant c.390–2A>G was confirmed to cause exon 6 skipping. We designed two ASOs and identified one of them that efficiently induced pseudoexon exclusion.ConclusionWe reported two novel variants of the ABCB11 gene, c.76+29T>G and c.390-2A>G, in a PFIC2 infant, thereby expanding the genotype of PFIC2. Our findings provide evidence for ASOs as a therapeutic approach for PFIC2 patients carrying intronic variants.     

A new ABCB11 mutation in two Italian children with familial intrahepatic cholestasis

Progressive familial intrahepatic cholestasis (PFIC) syndromes are characterized by defects in transporters of conjugated bile acids into the bile canaliculus. Three genes (ATP8B1, ABCB11, ABCB4) are associated with the different forms, but no easy genotype–phenotype correlations help in the prioritization for gene testing. We developed a denaturing high-performance liquid chromatography (DHPLC) method to screen patients with PFIC for mutations in ATP8B1 and ABCB11, and combined genetic analyses with immunolabeling in liver for the ABCB11 and ABCB4 gene products. Used in combination with commercially available antibodies on liver specimens, the DHPLC approach allowed us to confirm the clinical diagnosis in two Italian sisters and to identify a novel missesnse mutation in ABCB11. Our findings are expected to facilitate detection of the molecular cause of PFIC in affected families.     

Bile salt export pump deficiency disease: two novel,late onset,ABCB11 mutations identified by next generation sequencing

Progressive familial intrahepatic cholestasis (PFIC) is a heterogeneous group of autosomal recessive cholestatic diseases of childhood and represents the main indication for liver transplantation at this age; PFIC2 involves ABCB11 gene, that encodes the ATP-dependent canalicular bile salt export pump (BSEP). Benign intrahepatic cholestasis (BRIC) identifies a group of diseases involving the same genes and characterized by intermittent attacks of cholestasis with no progression to liver cirrhosis. Diagnosis with standard sequencing techniques is expensive and available only at a few tertiary centers. We report the application of next generation sequencing (NGS) in the diagnosis of the familial intrahepatic cholestasis with a parallel sequencing of three causative genes. We identified the molecular defects in ABCB11 gene in two different probands who developed a severe cholestatic disease of unknown origin. In the first patient a compound heterozygosity for the novel frameshift mutation p.Ser1100GlnfsX38 and the missense variant p.Glu135Lys was detected. In the second patient, triggered by contraceptive therapy, we identified homozygosity for a novel mis-sense variant p.Ala523Gly. In conclusion, these mutations seem to have a late onset and a less aggressive clinical impact, acting as an intermediate form between BRIC and PFIC.     

Bile acid-CoA ligase deficiency—a new inborn error of bile acid metabolism

Born at 27 weeks gestation, a child of consanguineous parents of Pakistani origin required prolonged parenteral nutrition. She developed jaundice, with extensive fibrosis and architectural distortion at liver biopsy; jaundice resolved with supportive care. Serum γ-glutamyl transpeptidase values were within normal ranges. The bile acids in her plasma and urine were >85% unconjugated (non-amidated). Two genes encoding bile-acid amidation enzymes were sequenced. No mutations were found in BAAT, encoding bile acid-CoA : aminoacid N-acyl transferase. The patient was homozygous for the missense mutation c.1012C > T in SLC27A5, predicted to alter a highly conserved amino-acid residue (p.H338Y) in bile acid-CoA ligase (BACL). She also was homozygous for the missense mutation c.1772A > G in ABCB11, predicted to alter a highly conserved amino-acid residue (p.N591S) in bile salt export pump (BSEP). BACL is essential for reconjugation of bile acids deconjugated by gut bacteria, and BSEP is essential for hepatocyte-canaliculus export of conjugated bile acids. A female sibling born at term had the same bile-acid phenotype and SLC27A5 genotype, without clinical liver disease. She was heterozygous for the c.1772A > G ABCB11 mutation. This is the first report of a mutation in SLC27A5. The amidation defect may have contributed to cholestatic liver disease in the setting of prematurity, parenteral nutrition, and homozygosity for an ABCB11 mutation.     

Prenatal diagnosis of progressive familial intrahepatic cholestasis type 2

Background and Aim:  Progressive familial intrahepatic cholestasis type 2 (PFIC2) results from genetic defects of the hepatobiliary bile salt export pump (BSEP, ABCB11 ) at chromosome 2q24. Patients with progressive cholestasis and liver cirrhosis usually need liver transplantation in the first decade. Mutations in ABCB11 are also associated with benign recurrent intrahepatic cholestasis type 2 and intrahepatic cholestasis of pregnancy in adult patients. We aimed to make the prenatal diagnosis of PFIC2.
Methods:  Genetic diagnosis was performed by genomic DNA analysis. Prenatal genetic diagnosis was made by fetal amniotic DNA and chorionic DNA analysis.
Results:  We report on two families of PFIC2 with inherited compound heterozygous mutations of ABCB11 (M183V and R303K in Family 1, V284L and 1145delC in Family 2) from the parents. An infant with heterozygous M183V mutation was later born healthy in Family 1. A fetus with compound heterozygous missense mutation V284L and 1145delC was terminated in Family 2.
Conclusion:  Prenatal diagnosis of PFIC2 was helpful to prevent further affected children in families with this fatal disease.     

ABCB11 gene mutations in Chinese children with progressive intrahepatic cholestasis and low γ glutamyltransferase

Background: Progressive familial intrahepatic cholestasis type 2 (PFIC2) is a severe autosomal recessive liver disorder of childhood that can cause cholestasis and progress to end‐stage liver disease. ABCB11 gene mutations causing PFIC2 have been reported in some population groups, but not in mainland Chinese. Aims: To elucidate the existence of and characterize ABCB11 gene mutations in mainland Chinese with progressive intrahepatic cholestasis and low γ glutamyltransferase (GGT). Methods: Twenty‐four children presenting with progressive intrahepatic cholestasis and low GGT were admitted to a tertiary paediatric hospital in eastern China from January 2004 to July 2007. All encoding exons and flanking areas of the ABCB11 gene were sequenced. Hepatic histopathology results were obtained by review of the medical record. Results: Twelve novel mutations of ABCB11 gene were found in seven patients: three nonsense mutations, six missense mutations, two splicing mutations and one intronic mutation. Giant cell transformation of hepatocytes was demonstrated in all the four patients with ABCB11 mutations and four of 12 patients without mutations in coding sequences of ABCB11 gene who received liver needle biopsy. Conclusions: ABCB11 gene mutations play an important role in Chinese patients with progressive intrahepatic cholestasis and low GGT. The characteristics of ABCB11 gene mutations in Chinese are different from other population groups. Histological examination may be helpful in diagnosis of PFIC2.     

A Rare BSEP Mutation Associated with a Mild Form of Progressive Familial Intrahepatic Cholestasis Type 2

Progressive Familial Intrahepatic Cholestasis type 2 (PFIC2) is a rare cholestatic disorder diagnosed in infancy or childhood that can lead to severe hepatic fibrosis and liver failure. Mutations in the ABCB11 gene result in a deficiency of the bile salt export protein (BSEP) and accumulation of bile inside the hepatocytes. Hepatocellular carcinoma is another condition associated with severe forms of deletion mutations in the ABCB11 gene. Treatment options including ursodeoxycholic acid biliary diversion have mixed outcomes and some patients require liver transplantation. Here, we describe two siblings with an extremely mild form of PFIC2 inherited from heterozygous parents. The elder sibling had acute liver failure at the age of six months and both siblings had pruritus, cholestasis, coagulopathy and fat-soluble-vitamin deficiencies in infancy but have been asymptomatic past infancy. Genetic testing of the siblings revealed that each were compound heterozygotes for two missense mutations of the ABCB11 gene: p.C68Y and p.R832H. Medical treatment typical for PFIC2 has not been necessary for either patient. This is the first report of these variants following a mild course in two affected patients.     

Hepatocanalicular bile salt export pump deficiency in patients with progressive familial intrahepatic cholestasis

BACKGROUND & AIMS: Progressive familial intrahepatic cholestasis (PFIC), an inherited liver disease of childhood, is characterized by cholestasis and either normal or increased serum gamma-glutamyltransferase activity. Patients with normal gamma-glutamyltransferase activity have mutations of the FIC1 locus on chromosome 18q21 or mutations of the BSEP gene on chromosome 2q24. Also, patients with bile acid synthesis defects have low gamma-glutamyltransferase activity. We investigated expression of the bile salt export pump (BSEP) in liver samples from patients with a PFIC phenotype and correlated this with BSEP gene mutations. METHODS: BSEP and multidrug resistance protein 2 (MRP2) expressions were studied by immunohistochemistry in liver specimens of 28 patients and BSEP gene mutation analysis in 19 patients. Bile salt kinetics were studied in 1 patient. RESULTS: Sixteen of 28 liver samples showed no canalicular BSEP staining. Staining for MRP2 showed a normal canalicular pattern in all but 1 of these samples. Ten of 19 patients showed BSEP gene mutations; BSEP protein expression was lacking in all 10 patients. No mutations were found in 9 of 19 patients, and in all except 1, BSEP protein expression was normal. Bile salt concentration in bile of BSEP-negative/MRP2-positive PFIC patients was 0.2 +/- 0.2 mmol/L (n = 9; <1% of normal) and in BSEP-positive PFIC patients 18.1 +/- 9.9 mmol/L (n = 3; 40% of normal). The kinetic study confirmed the dramatic decrease of bile salt secretion in BSEP-negative patients. CONCLUSIONS: The findings show a close correlation between BSEP gene mutations and canalicular BSEP expression. Biliary secretion of bile salts is greatly reduced in BSEP-negative patients.     

Two common PFIC2 mutations are associated with the impaired membrane trafficking of BSEP/ABCB11

Progressive familial intrahepatic cholestasis type 2 (PFIC2) is caused by a mutation in the bile salt export pump (BSEP/ABCB11) gene. However, the mechanisms for the deficiency in the function of two mutations (E297G and D482G), which are frequently found in European patients, have not yet been identified. In the present study, we examined the transport activity and cellular localization of these two mutants in human embryonic kidney 293 and Madin-Darby canine kidney II cells, respectively. Introduction of E297G and D482G mutations into the human BSEP gene by site-directed mutagenesis resulted in a significant reduction in the BSEP expression level, which was associated with impaired membrane trafficking. Most of the D482G BSEP and some of the E297G BSEP underwent only core glycosylation and appeared to be predominantly located in the endoplasmic reticulum. The inhibition of proteasome function by MG132 resulted in the cellular accumulation of the core glycosylation form of the two mutants. In contrast, transport studies for taurocholate and glycocholate with membrane vesicles isolated from complementary DNA-transfected cells indicated that both mutations did not significantly affect the transport function of BSEP per se. In conclusion, E297G and D482G mutations result in impaired membrane trafficking, whereas the transport functions of these mutants remain largely unchanged.     

Paediatric hepatocellular carcinoma due to somatic CTNNB1 and NFE2L2 mutations in the setting of inherited bi-allelic ABCB11 mutations

Hepatocellular carcinoma (HCC) rarely occurs in childhood. We describe a patient with new onset of pruritus at 8 months of age who at 17 months of age was found to have a 2.5 cm HCC. To delineate the possible genetic basis of this tumour, we performed whole exome sequencing (WES) of the germline DNA and identified two novel predictably deleterious missense mutations in ABCB11, encoding bile salt export pump (BSEP), confirmed in the parental DNA as bi-allelic and inherited. Although inherited ABCB11 mutations have previously been linked to HCC in a small number of cases, the molecular mechanisms of hepatocellular carcinogenesis in ABCB11 disease are unknown. WES of the HCC tissue uncovered somatic driver mutations in the beta-catenin (CTNNB1) and nuclear-factor-erythroid-2-related-factor-2 (NFE2L2) genes. Moreover, clonality analysis predicted that the CTNNB1 mutation was clonal and occurred earlier during carcinogenesis, whereas the NFE2L2 mutation was acquired later. Interestingly, background liver parenchyma showed no inflammation or fibrosis and BSEP expression was preserved. This is the first study to identify somatic CTNNB1 and NFE2L2 mutations in early childhood arisen in the setting of inherited bi-allelic ABCB11 mutations. Rapid WES analysis expedited this child’s diagnosis and treatment, and likely improved her prognosis.     

Hereditäre Defekte hepatobiliärer Transportproteine

Defects in transport proteins that are expressed at the hepatocyte canalicular membrane can cause severe impairment of hepatobiliary transport processes. Progressive familial intrahepatic cholestasis (PFIC) typically manifests in early childhood. Genetic variants in the aminophospholipid transporter FIC1 (ATP8B1 gene) cause PFIC1, characterized by elevated serum bile acids but normal or only mildly elevated gamma-GT levels. Benign recurrent intrahepatic cholestasis type 1 (BRIC1) is also caused by ATP8B1 mutations. Defects in the function of the bile salt efflux pump (BSEP; ABCB11) cause PFIC2 or BRIC2, depending on the degree of BSEP impairment. A common BSEP variant, the V444A polymorphism, is commonly found in various types of cholestatic liver injury, including drug-induced liver injury. Finally, dysfunction of the multidrug resistance gene product MDR3 (ABCB4) leads to PFIC3, characterized by low biliary phospholipids and high gamma-GT levels in serum due to bile duct injury. All three transporter genes are also associated with intrahepatic cholestasis of pregnancy. Treatment options include ursodeoxycholic acid for milder forms and liver transplantation for severe pediatric cases.     

Gradual improvement of liver function after administration of ursodeoxycholic acid in an infant with a novel ABCB11 gene mutation with phenotypic continuum between BRIC2 and PFIC2

OBJECT: The authors report the case of a boy with PFIC type 2 or BRIC type 2 who suffered from liver dysfunction at 2 months after birth. METHODS AND RESULTS: A liver biopsy specimen revealed mild liver cirrhosis, and the findings resembled those observed in Byler disease. Genetic examination revealed a normal familial intrahepatic cholestasis-1 gene, but a heterozygous mutation for the ABCB11, C1620A (F540L), was observed. Therefore, the patient was initially diagnosed with PFIC type 2. For 3 years after the diagnosis, he had severe pruritus, an increased serum bile acid, and normal serum values of gamma-glutamyl transaminase. At the age of 2, treatment with administration of ursodeoxycholic acid was started; subsequently, a gradual improvement in his liver function was observed. At the age of 3, he suffered from massive intestinal and pulmonary hemorrhage, which improved immediately after the administration of vitamin K. He was then admitted to our hospital for liver transplantation. At 1 month after the admission, his liver dysfunction showed further improvement, except for a mild increase in the serum bile acid level. This condition did not show any change during the 5-year follow-up period. In addition, the patient showed severe growth failure and was diagnosed with growth hormone deficiency. Hence, he receives growth hormone administration. CONCLUSION: The patient could be genetically diagnosed with bile salt export pump disease of PFIC type 2 or BRIC type 2. Various clinical features are observed in PFIC or BRIC patients with ABCB11 mutation.     

Successful pregnancy after ileal exclusion in progressive familial intrahepatic cholestasis type 2

Progressive familial intrahepatic cholestasis type 2 (PFIC 2) results from mutations in ABCB11 gene coding bile salt export pump (BSEP). Medical treatment is usually unsuccessful and surgery intervention is necessary. Partial external biliary diversion (PEBD) is regarded as the first choice of surgical treatment. Ileal exclusion (IE) is an alternative operation if external stoma is not tolerated; however, a favorable outcome is uncertain. In chronic liver diseases pregnancy brings additional risk of deterioration of liver function and generally is not recommended. We present the first case report of successful pregnancy in a genetically confirmed PFIC 2 patient after surgical conversion from PEBD to IE.