J Byrne

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. (HEPATOLOGY 2006;44:478–486.)

Severe bile salt export pump deficiency : 82 different ABCB11 mutations in 109 families

BACKGROUND & AIMS Patients with severe bile salt export pump (BSEP) deficiency present as infants with progressive cholestatic liver disease. We characterized mutations of ABCB11 (encoding BSEP) in such patients and correlated genotypes with residual protein detection and risk of malignancy. METHODS Patients with intrahepatic cholestasis suggestive of BSEP deficiency were investigated by single-strand conformation polymorphism analysis and sequencing of ABCB11. Genotypes sorted by likely phenotypic severity were correlated with data on BSEP immunohistochemistry and clinical outcome. RESULTS Eighty-two different mutations (52 novel) were identified in 109 families (9 nonsense mutations, 10 small insertions and deletions, 15 splice-site changes, 3 whole-gene deletions, 45 missense changes). In 7 families, only a single heterozygous mutation was identified despite complete sequence analysis. Thirty-two percent of mutations occurred in >1 family, with E297G and/or D482G present in 58% of European families (52/89). On immunohistochemical analysis (88 patients), 93% had abnormal or absent BSEP staining. Expression varied most for E297G and D482G, with some BSEP detected in 45% of patients (19/42) with these mutations. Hepatocellular carcinoma or cholangiocarcinoma developed in 15% of patients (19/128). Two protein-truncating mutations conferred particular risk; 38% (8/21) of such patients developed malignancy versus 10% (11/107) with potentially less severe genotypes (relative risk, 3.7 [confidence limits, 1.7-8.1; P = .003]). CONCLUSIONS With this study, >100 ABCB11 mutations are now identified. Immunohistochemically detectable BSEP is typically absent, or much reduced, in severe disease. BSEP deficiency confers risk of hepatobiliary malignancy. Close surveillance of BSEP-deficient patients retaining their native liver, particularly those carrying 2 null mutations, is essential.

Characterization of mutations in ATP8B1 associated with hereditary cholestasis

Progressive familial intrahepatic cholestasis (PFIC) and benign recurrent intrahepatic cholestasis (BRIC) are clinically distinct hereditary disorders. PFIC patients suffer from chronic cholestasis and develop liver fibrosis. BRIC patients experience intermittent attacks of cholestasis that resolve spontaneously. Mutations in ATP8B1 (previously FIC1) may result in PFIC or BRIC. We report the genomic organization of ATP8B1 and mutation analyses of 180 families with PFIC or BRIC that identified 54 distinct disease mutations, including 10 mutations predicted to disrupt splicing, 6 nonsense mutations, 11 small insertion or deletion mutations predicted to induce frameshifts, 1 large genomic deletion, 2 small inframe deletions, and 24 missense mutations. Most mutations are rare, occurring in 1–3 families, or are limited to specific populations. Many patients are compound heterozygous for 2 mutations. Mutation type or location correlates overall with clinical severity: missense mutations are more common in BRIC (58% vs. 38% in PFIC), while nonsense, frameshifting, and large deletion mutations are more common in PFIC (41% vs. 16% in BRIC). Some mutations, however, lead to a wide range of phenotypes, from PFIC to BRIC or even no clinical disease. ATP8B1 mutations were detected in 30% and 41%, respectively, of the PFIC and BRIC patients screened. Supplementary material for this article can be found on the HEPATOLOGY website (http://interscience.wiley.com/jpages/0270‐9139/suppmat/index.html) and at www.atp8b1‐primers.nl (HEPATOLOGY 2004;40:27–38.)

Missense mutations and single nucleotide polymorphisms in ABCB11 impair bile salt export pump processing and function or disrupt pre‐messenger RNA splicing

The gene encoding the human bile salt export pump (BSEP), ABCB11, is mutated in several forms of intrahepatic cholestasis. Here we classified the majority (63) of known ABCB11 missense mutations and 21 single‐nucleotide polymorphisms (SNPs) to determine whether they caused abnormal ABCB11 pre‐messenger RNA splicing, abnormal processing of BSEP protein, or alterations in BSEP protein function. Using an in vitro minigene system to analyze splicing events, we found reduced wild‐type splicing for 20 mutations/SNPs, with normal mRNA levels reduced to 5% or less in eight cases. The common ABCB11 missense mutation encoding D482G enhanced aberrant splicing, whereas the common SNP A1028A promoted exon skipping. Addition of exogenous splicing factors modulated several splicing defects. Of the mutants expressed in vitro in CHO‐K1 cells, most appeared to be retained in the endoplasmic reticulum and degraded. A minority had BSEP levels similar to wild‐type. The SNP variant A444 had reduced levels of protein compared with V444. Treatment with glycerol and incubation at reduced temperature overcame processing defects for several mutants, including E297G. Taurocholate transport by two assessed mutants, N490D and A570T, was reduced compared with wild‐type. Conclusion: This work is a comprehensive analysis of 80% of ABCB11 missense mutations and single‐nucleotide polymorphisms at pre‐mRNA splicing and protein processing/functional levels. We show that aberrant pre‐mRNA splicing occurs in a considerable number of cases, leading to reduced levels of normal mRNA. Thus, primary defects at either the protein or the mRNA level (or both) contribute significantly to BSEP deficiency. These results will help to develop mutation‐specific therapies for children and adults suffering from intrahepatic cholestasis due to BSEP deficiency. (HEPATOLOGY 2008.)

Effect of Ischemic Preconditioning on the Genomic Response to Reperfusion Injury in Deceased Donor Liver Transplantation

Ischemic preconditioning (IP) is an effective method for protecting organs from ischemia/reperfusion (IR) injury; however, the molecular basis of this protective effect is poorly understood. This study assessed the gene expression profile in liver allografts during transplantation and evaluated the impact of IP. Prereperfusion and postreperfusion biopsy specimens from livers subjected to IP (n = 19) or no preconditioning (the IR group; n = 16) were obtained. Total RNA was extracted and hybridized to GeneChip microarrays, and the findings were validated with real‐time quantitative reverse‐transcription polymerase chain reaction (qRT‐PCR). IP livers showed less of an increase in aspartate aminotransferase after transplantation. A microarray analysis of the IR group showed increased expression of 57 genes mainly involved in cell death, inflammation and immune response, stress, and modulation of the cell cycle. The IP group showed attenuation of the expression of these genes after reperfusion. Additionally, IP led to increased expression of 43 genes involved in growth and maintenance, cell‐cycle regulation, proliferation, and development. The expression of the 12 most significant genes was validated in all patients with real‐time qRT‐PCR, and the fold changes of a number of genes correlated with clinical parameters and graft outcomes. IP protection of liver allografts was associated with a reduction in the expression of immune response genes and promotion of those involved in protection and repair. Liver Transpl 15:1750–1765, 2009.

Lack of hepatocellular CD10 along bile canaliculi is physiologic in early childhood and persistent in Alagille syndrome.

Many tissues, including hepatobiliary cells, express neutral endopeptidase (CD10), encoded by MME. Serum neutral endopeptidase activity (NEA) has been recommended as a marker of cholestasis in adults but not in children with Alagille syndrome (AGS). We investigated ontogenic and disease-related differences in the expression of CD10. CD10 was found on canalicular surfaces of hepatocytes throughout the lobule in 16 adults and in 31 children aged ≥24 months, with and without cholestasis, but not in 39 children aged <24 months, with and without cholestasis. Ten AGS children aged 2 months to 6 years lacked any canalicular CD10 expression. Cholangiocyte apices and/or intrasinusoidal granulocytes marked for CD10 in all subjects. Liver membrane fractions from a child with cholestasis aged <24 months and from 2 AGS patients aged >24 months contained reduced levels of CD10. In contrast, AGS children and all controls expressed CD10 similarly on granulocytes. MME mRNA was found in the liver of children aged <24 months and of adults, all with cholestasis, and of AGS patients. Granulocyte MME mRNA levels were similar among all study subjects; however, liver MME mRNA levels were 6- to 140-fold less than in normal adults in all cholestatic subjects, including AGS children. Methylation of the MME promoter was not detected in the liver of AGS children. In conclusion, hepatocytes in early childhood physiologically lack immunohistochemically detectable CD10. Reduced MME mRNA in AGS is not due to MME promoter methylation. Liver CD10 in childhood appears to undergo reduced synthesis or rapid degradation, which persists in AGS. Absence of CD10 expression thus may limit NEA as a marker of cholestasis in young patients and in AGS.

ATP8B1 gene expression is driven by a housekeeping-like promoter independent of bile acids and farnesoid X receptor.

Background Mutations in ATP8B1 gene were identified as a cause of low γ-glutamyltranspeptidase cholestasis with variable phenotype, ranging from Progressive Familial Intrahepatic Cholestasis to Benign Recurrent Intrahepatic Cholestasis. However, only the coding region of ATP8B1 has been described. The aim of this research was to explore the regulatory regions, promoter and 5′untranslated region, of the ATP8B1 gene. Methodology/Principal Findings 5′Rapid Amplification of cDNA Ends using human liver and intestinal tissue was performed to identify the presence of 5′ untranslated exons. Expression levels of ATP8B1 transcripts were determined by quantitative reverse-transcription PCR and compared with the non-variable part of ATP8B1. Three putative promoters were examined in vitro using a reporter gene assay and the main promoter was stimulated with chenodeoxycholic acid. Four novel untranslated exons located up to 71 kb upstream of the previously published exon 1 and twelve different splicing variants were found both in the liver and the intestine. Multiple transcription start sites were identified within exon −3 and the proximal promoter upstream of this transcription start site cluster was proven to be an essential regulatory element responsible for 70% of total ATP8B1 transcriptional activity. In vitro analysis demonstrated that the main promoter drives constitutive ATP8B1 gene expression independent of bile acids. Conclusions/Significance The structure of the ATP8B1 gene is complex and the previously published transcription start site is not significant. The basal expression of ATP8B1 is driven by a housekeeping-like promoter located 71 kb upstream of the first protein coding exon.

Outcomes of surgical management of familial intrahepatic cholestasis 1 and bile salt export protein deficiencies

Progressive familial intrahepatic cholestasis (PFIC) with normal circulating gamma‐glutamyl transpeptidase levels can result from mutations in the ATP8B1 gene (encoding familial intrahepatic cholestasis 1 [FIC1] deficiency) or the ABCB11 gene (bile salt export protein [BSEP] deficiency). We investigated the outcomes of partial external biliary diversion, ileal exclusion, and liver transplantation in these two conditions. We conducted a retrospective multicenter study of 42 patients with FIC1 deficiency (FIC1 patients) and 60 patients with BSEP deficiency (BSEP patients) who had undergone one or more surgical procedures (57 diversions, 6 exclusions, and 57 transplants). For surgeries performed prior to transplantation, BSEP patients were divided into two groups, BSEP‐common (bearing common missense mutations D482G or E297G, with likely residual function) and BSEP‐other. We evaluated clinical and biochemical outcomes in these patients. Overall, diversion improved biochemical parameters, pruritus, and growth, with substantial variation in individual response. BSEP‐common or FIC1 patients survived longer after diversion without developing cirrhosis, being listed for or undergoing liver transplantation, or dying, compared to BSEP‐other patients. Transplantation resolved cholestasis in all groups. However, FIC1 patients commonly developed hepatic steatosis, diarrhea, and/or pancreatic disease after transplant accompanied by biochemical abnormalities and often had continued poor growth. In BSEP patients with impaired growth, this generally improved after transplantation. Conclusion: Diversion can improve clinical and biochemical status in FIC1 and BSEP deficiencies, but outcomes differ depending on genetic etiology. For many patients, particularly BSEP‐other, diversion is not a permanent solution and transplantation is required. Although transplantation resolves cholestasis in patients with FIC1 and BSEP deficiencies, the overall outcome remains unsatisfactory in many FIC1 patients; this is mainly due to extrahepatic manifestations. (Hepatology Communications 2018;2:515‐528)