Clinical features and genotype-phenotype correlations in children with progressive familial intrahepatic cholestasis type 3 related to ABCB4 mutations

Clinical and genetic study of ABCB4 gene-related cholestatic liver disease in China: children and adults

BACKGROUND

ABCB4 gene-related cholestatic liver diseases have a wide spectrum of clinical and genetic variations. The correlation between genotype and clinical phenotype still unclear. This study retrospectively analyzed the clinical and pathological characteristics of 23 patients with ABCB4 gene-related cholestatic liver diseases. Next-generation sequencing was used to identify the genetic causes.

RESULTS

The 23 included patients (15 children and 8 adults) were diagnosed as progressive familial intrahepatic cholestasis type 3 (PFIC3), drug-induced liver injury (DILI), cirrhosis cholestasis, cirrhosis, and mild liver fibrosis. Nineteen patients underwent liver pathological examination of the liver, exhibiting fibrosis, small bile duct hyperplasia, CK7(+), Cu(+), bile duct deletion, and cirrhosis. Thirty ABCB4 variants were identified, including 18 novel variants.

CONCLUSION

ABCB4 gene-related cholestatic liver diseases have a wide spectrum of clinical and genetic variations. Biallelic ABCB4 mutation carriers tended to severe PFIC3, which mostly occurs in children; while ABCB4 non-biallelic variants can lead to milder ICP, LACP, DILI or overlapping, mostly in adults. Thus, the ABCB4 genotype has a specific correlation with the phenotype, but there are exceptions. Non-biallelic null mutations can cause severe diseases. The mechanisms underlying this genetic phenotype require further investigation.

UK guideline on the transition and management of childhood liver diseases in adulthood

INTRODUCTION

Improved outcomes of liver disease in childhood and young adulthood have resulted in an increasing number of young adults (YA) entering adult liver services. The adult hepatologist therefore requires a working knowledge in diseases that arise almost exclusively in children and their complications in adulthood.

AIMS

To provide adult hepatologists with succinct guidelines on aspects of transitional care in YA relevant to key disease aetiologies encountered in clinical practice.

METHODS

A systematic literature search was undertaken using the Pubmed, Medline, Web of Knowledge and Cochrane database from 1980 to 2023. MeSH search terms relating to liver diseases ('cholestatic liver diseases', 'biliary atresia', 'metabolic', 'paediatric liver diseases', 'autoimmune liver diseases'), transition to adult care ('transition services', 'young adult services') and adolescent care were used. The quality of evidence and the grading of recommendations were appraised using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) system.

RESULTS

These guidelines deal with the transition of YA and address key aetiologies for the adult hepatologist under the following headings: (1) Models and provision of care; (2) screening and management of mental health disorders; (3) aetiologies; (4) timing and role of liver transplantation; and (5) sexual health and fertility.

CONCLUSIONS

These are the first nationally developed guidelines on the transition and management of childhood liver diseases in adulthood. They provide a framework upon which to base clinical care, which we envisage will lead to improved outcomes for YA with chronic liver disease.

Outcomes of 38 patients with PFIC3: Impact of genotype and of response to ursodeoxycholic acid therapy

Background & Aims

Progressive familial intrahepatic cholestasis type 3 (PFIC3) is a rare liver disease caused by biallelic variations in ABCB4. Data reporting on the impact of genotype and of response to ursodeoxycholic acid (UDCA) therapy on long-term outcomes are scarce.

Methods

We retrospectively describe a cohort of 38 patients with PFIC3 with a median age at last follow-up of 19.5 years (range 3.8-53.8).

Results

Twenty patients presented with symptoms before 1 year of age. Thirty-one patients received ursodeoxycholic acid (UDCA) therapy resulting in serum liver test improvement in 20. Twenty-seven patients had cirrhosis at a median age of 8.1 years of whom 18 received a liver transplant at a median age of 8.5 years. Patients carrying at least one missense variation were more likely to present with positive (normal or decreased) canalicular MDR3 expression in the native liver and had prolonged native liver survival (NLS; median 12.4 years [range 3.8-53.8]). In contrast, in patients with severe genotypes (no missense variation), there was no detectable canalicular MDR3 expression, symptom onset and cirrhosis occurred earlier, and all underwent liver transplantation (at a median age of 6.7 years [range 2.3-10.3]). The latter group was refractory to UDCA treatment, whereas 87% of patients with at least one missense variation displayed an improvement in liver biochemistry in response to UDCA. Biliary phospholipid levels over 6.9% of total biliary lipid levels predicted response to UDCA. Response to UDCA predicted NLS.

Conclusions

Patients carrying at least one missense variation, with positive canalicular expression of MDR3 and a biliary phospholipid level over 6.9% of total biliary lipid levels were more likely to respond to UDCA and to exhibit prolonged NLS.

Impact and implications

In this study, data show that genotype and response to ursodeoxycholic acid therapy predicted native liver survival in patients with PFIC3 (progressive familial intrahepatic cholestasis type 3). Patients carrying at least one missense variation, with positive (decreased or normal) immuno-staining for canalicular MDR3, and a biliary phospholipid level over 6.9% of total biliary lipids were more likely to respond to ursodeoxycholic acid therapy and to exhibit prolonged native liver survival.

Variable Intrafamilial Expression of ABCB4 Disease

Progressive familial intrahepatic cholestasis type 3 (PFIC3) is a rare cholestatic liver disease with autosomal recessive inheritance caused by mutations in the ABCB4 gene. The clinical presentation of PFIC3 varies significantly, displaying incomplete penetrance without clear genotype-phenotype correlations. As such, the suitability of living-related liver donation for children with advanced disease has been questioned. We report here the long-term follow-up of a patient with PFIC3 resulting in decompensated cirrhosis at 11 years who successfully underwent living donor liver transplantation from his father, who carried the same ABCB4 homozygous mutation.

Ivacaftor-Mediated Potentiation of ABCB4 Missense Mutations Affecting Critical Motifs of the NBDs: Repositioning Perspectives for Hepatobiliary Diseases

ABCB4 (ATP-binding cassette subfamily B member 4) is a hepatocanalicular floppase involved in biliary phosphatidylcholine (PC) secretion. Variations in the ABCB4 gene give rise to several biliary diseases, including progressive familial intrahepatic cholestasis type 3 (PFIC3), an autosomal recessive disease that can be lethal in the absence of liver transplantation. In this study, we investigated the effect and potential rescue of ten ABCB4 missense variations in NBD1:NBD2 homologous positions (Y403H/Y1043H, K435M/K1075M, E558K/E1200A, D564G/D1206G and H589Y/H1231Y) all localized at the conserved and functionally critical motifs of ABC transporters, six of which are mutated in patients. By combining structure analysis and in vitro studies, we found that all ten mutants were normally processed and localized at the canalicular membrane of HepG2 cells, but showed dramatically impaired PC transport activity that was significantly rescued by treatment with the clinically approved CFTR potentiator ivacaftor. Our results provide evidence that functional ABCB4 mutations are rescued by ivacaftor, paving the way for the repositioning of this potentiator for the treatment of selected patients with PFIC3 caused by mutations in the ATP-binding sites of ABCB4.

Clinical and genetic characterization of pediatric patients with progressive familial intrahepatic cholestasis type 3 (PFIC3): identification of 14 novel ABCB4 variants and review of the literatures

BACKGROUND

Progressive familial intrahepatic cholestasis type 3 (PFIC3) is an autosomal recessive disease caused by pathogenic variants of the gene ABCB4. This study aimed to investigate the ABCB4 genotypic and the clinical phenotypic features of PFIC3 patients.

METHODS

The clinical and molecular genetic data of 13 new pediatric patients with PFIC3 as well as 82 reported ones in the PubMed and CNKI databases were collected and analyzed.

RESULTS

The 13 new PFIC3 patients included six females and seven males, and the main presentations were hepatomegaly, splenomegaly, jaundice, and pruritus, as well as increased levels of gamma-glutamyl transpeptidase (GGT). Fourteen new ABCB4 variants were detected, including eight diagnosed to be likely-pathogenic and six, pathogenic. Among all the 95 PFIC3 cases, hepatomegaly was observed in 85.3% (81/95), pruritus in 67.4% (64/95), splenomegaly in 52.6% (50/95), jaundice in 48.4% (46/95), portal hypertension in 34.7% (33/95) and GGT elevation in 100% (88/88) of the patients. Positive responses at varied degrees to oral ursodeoxycholic acid (UDCA) treatment were observed in 66.1% (39/59) of the patients, among whom 38.5% (15/39) fully recovered in terms of the laboratory changes. Although the condition remained stable in 53 patients (58.9%, 53/90), the clinical outcomes were not promising in the rest 37 cases (41.1%, 37/90), including 7 died, 27 having undergone while another 3 waiting for liver transplantation. A total of 96 ABCB4 variants were detected in the 95 patients. PFIC3 patients with biallelic null variants exhibited earlier onset ages [10.5 (2, 18) vs. 19 (8, 60) months, p = 0.007], lower UDCA response rate [18.2% (2/11) vs. 77.1% (37/48), p = 0.001], and more unpromising clinical outcomes [80% (12/15) vs. 33.3% (25/75), p = 0.001], compared with those with non-biallelic null variants.

CONCLUSIONS

PFIC3 presented with hepatomegaly, pruritus, splenomegaly and jaundice with increased serum GGT level as a biochemistry hallmark. Although varying degrees of improvement in response to UDCA therapy were observed, 41.1% of PFIC3 patients exhibited unfavorable prognosis. ABCB4 genotypes of biallelic null variants were associated with severer PFIC3 phenotypes. Moreover, the 14 novel variants in this study expanded the ABCB4 mutation spectrum, and provided novel molecular biomarkers for diagnosis of PFIC3 patients.

Clinical phenotype of adult-onset liver disease in patients with variants in ABCB4, ABCB11, and ATP8B1

Variants in ATP8B1, ABCB11, and ABCB4 underlie the most prevalent forms of progressive familial intrahepatic cholestasis. We aim to describe variants in these genes in a cohort of patients with adult‐onset liver disease, and explore a genotype–phenotype correlation. Patients with onset of liver disease aged above 18 who underwent sequencing of cholestasis genes for clinical purposes over a 5‐year period were identified. Bioinformatic analysis of variants was performed. Liver histology was evaluated in patients with variants. Of the 356 patients tested, at least one variant was identified in 101 (28.4%): 46 ABCB4, 35 ABCB11, and 28 ATP8B1. Patients with ABCB4 variants had chronic liver disease (71.7%) and pregnancy‐associated liver dysfunction (75%), with a younger age of onset in more severe genotypes (p = 0.046). ABCB11 variants presented with pregnancy‐associated liver dysfunction (82.4%) and acute/episodic cholestasis (40%), with no association between age of onset and genotype severity. ATP8B1 variants were associated with chronic liver disease (75%); however, they were commonly seen in patients with an alternate etiology of liver disease and variants were of low predicted pathogenicity. In adults with suspected genetic cholestasis, variants in cholestasis genes were frequently identified and were likely to contribute to the development of liver disease, particularly ABCB4 and ABCB11. Variants were often in heterozygous state, and they should no longer be considered recessive Mendelian traits. Sequencing cholestasis genes in selected patients with adult‐onset disease should be considered, with interpretation in close collaboration with histopathologists and geneticists.

Variants in cholestasis genes were found in patients with adult‐onset liver disease. ABCB4 variants are associated with chronic biliary disease, variants in ABCB11 are seen in patients with acute cholestasis, and the clinical significance of ATP8B1 variants is not clear.

Progressive familial intrahepatic cholestasis type 3: Report of four clinical cases, novel ABCB4 variants and long-term follow-up

INTRODUCTION AND OBJECTIVES

Progressive familial intrahepatic cholestasis type 3 (PFIC-3) is a rare autosomal recessive cholestatic liver disorder caused by mutations in the ABCB4 gene. The aim of this study was to present the phenotypic and genotypic spectrum of 4 Polish PFIC-3 patients diagnosed in a one-referral centre.

MATERIALS AND METHODS

The study included 4 patients with cholestasis and pathogenic variants in the ABCB4 gene identified by next-generation sequencing (NGS) of a targeted-gene panel or whole exome sequencing (WES). Clinical, laboratory, histological, and molecular data were collected.

RESULTS

Four patients (three males) were identified. The age at first noted clinical signs and symptoms was 6, 2.5, 14, and 2 years respectively; the mean age was 6 years. Those signs and symptoms include pruritus (2 out of 4 patients) and hepatomegaly with splenomegaly (4 out of 4 patients). The age at the time of referral to our centre was 9, 3, 15, and 2.5 years respectively, while the mean age was 7 years. Chronic cholestatic liver disease of unknown aetiology was established in all of them. The NGS analysis was performed in all patients at the last follow-up visit. Three novel variants including c.902T>A, p.Met301Lys, c.3279+1G>A, p.?, and c.3524T>A, p.Leu1175His were identified. The time from the first consultation to the final diagnosis was 14, 9, 3, and 1 year respectively; the mean was 6.8 years. A detailed follow-up was presented.

CONCLUSIONS

The clinical phenotype of PFIC-3 could be variable. The clinical and biochemical diagnosis of PFIC-3 is difficult, thus the NGS study is very useful in making a proper diagnosis.

Clinical outcomes of surgical management for rare types of progressive familial intrahepatic cholestasis: a case series

Background

Progressive familial intrahepatic cholestasis (PFIC) is a heterogeneous group of genetic autosomal recessive diseases that cause severe cholestasis, which progresses to cirrhosis and liver failure, in infancy or early childhood. We herein report the clinical outcomes of surgical management in patients with four types of PFIC.

Case presentation

Six patients diagnosed with PFIC who underwent surgical treatment between 1998 and 2020 at our institution were retrospectively assessed. Living-donor liver transplantation (LDLT) was performed in 5 patients with PFIC. The median age at LDLT was 4.8 (range: 1.9–11.4) years. One patient each with familial intrahepatic cholestasis 1 (FIC1) deficiency and bile salt export pump (BSEP) deficiency died after LDLT, and the four remaining patients, one each with deficiency of FIC1, BSEP, multidrug resistance protein 3 (MDR3), and tight junction protein 2 (TJP2), survived. One FIC1 deficiency recipient underwent LDLT secondary to deterioration of liver function, following infectious enteritis. Although he underwent LDLT accompanied by total external biliary diversion, the patient died because of PFIC-related complications. The other patient with FIC1 deficiency had intractable pruritus and underwent partial internal biliary diversion (PIBD) at 9.8 years of age, pruritus largely resolved after PIBD. One BSEP deficiency recipient, who had severe graft damage, experienced recurrence of cholestasis due to the development of antibodies against BSEP after LDLT, and eventually died due to graft failure. The other patient with BSEP deficiency recovered well after LDLT and there was no evidence of posttransplant recurrence of cholestasis. In contrast, recipients with MDR3 or TJP2 deficiency showed good courses and outcomes after LDLT.

Conclusions

Although LDLT was considered an effective treatment for PFIC, the clinical courses and outcomes after LDLT were still inadequate in patients with FIC1 and BSEP deficiency. LDLT accompanied by total biliary diversion may not be as effective for patients with FIC1 deficiency.

ATP8B1, ABCB11, and ABCB4 Genes Defects: Novel Mutations Associated with Cholestasis with Different Phenotypes and Outcomes

OBJECTIVES

To characterize the clinical, laboratory, histologic, molecular features, and outcome of gene-confirmed progressive familial intrahepatic cholestasis (PFIC) 1-3 among Arabs and to evaluate for "genotype-phenotype" correlations.

STUDY DESIGN

We retrospectively reviewed charts of 65 children (ATP8B1 defect = 5, ABCB11 = 35, ABCB4 = 25) who presented between 2008 and 2019 with cholestasis. The clinical phenotype of a disease was categorized based on response of cholestasis and itching to ursodeoxycholic acid and ultimate outcome, into mild (complete response), intermediate (partial response, nonprogressive), and severe (progression to end-stage liver disease).

RESULTS

Overall, 27 different mutations were identified (ATP8B1, n = 5; ABCB11, n = 11; ABCB4, n = 11), comprising 10 novel ones. Six patients with heterozygous missense mutations (ATP8B1, n = 2; ABCB11, n = 4) had transient cholestasis. Of the remaining 3 patients with PFIC1, 2 developed severe phenotype (splicing and frameshift mutations). Of the remaining 31 patients with PFIC2, 25 developed severe disease (15 due to frameshift and splicing mutations). Of 25 patients with PFIC3, 10 developed a severe phenotype (1 splicing and 3 frameshift mutations; 6 missense). Patients with PFIC2 had significantly shorter survival time and more rapid disease progression than patients with PFIC3 (P < .001). Patients with frameshift mutations in ABCB11 gene (p.Thr127Hisfs∗6) and ABCB4 gene (p.Phe210Serfs∗5) had significantly shorter survival time than missense mutations (P = .011; P = .0039, respectively).

CONCLUSIONS

We identified genotype-phenotype correlations among mutations in ABCB11 and ABCB4 genes, which underscore the prognostic value of early genetic diagnosis. The disease course in patients with PFIC3 could be favorably modified by ursodeoxycholic acid therapy.

Common ABCB4 and ABCB11 Genotypes Are Associated with Idiopathic Chronic Cholestasis in Adults

INTRODUCTION

Pathogenic mutations in genes encoding the hepatocanalicular transporters ATP8B1, ABCB11 and ABCB4 are causative for progressive cholestatic liver disease in children. In adults, less severe variants such as the common ABCB4 c.711A>T polymorphism have been associated with intrahepatic cholestasis in pregnancy and elevated liver enzymes. Hence, our aim was to study the role of common polymorphisms in adult patients with chronic unexplained cholestasis.

METHODS

Screening of outpatients of two university hospitals identified a cohort of 94 patients with chronic cholestasis of unknown origin after thorough exclusion of other causes. Genotyping was performed using TaqMan assays, and frequencies for the ABCB4 rs2109505 (c.711A>T), rs1202283 (c.504T>C), ABCB11 rs2287622 (p.A444V) and rs497692 (c.3084A>G) variants of the study cohort were compared to a cohort of 254 healthy controls.

RESULTS

The dominating symptoms of the patients were pruritus and jaundice, though the majority of them did not report symptoms at inclusion. Advanced fibrosis or cirrhosis was present in 11 patients (11.7%) only. Genotyping revealed the presence of the ABCB4 c.711A>T risk variant in 79 patients (84%), a frequency that is significantly (p = 0.037) higher than that in controls (71%). The ABCB11 p.A444V variant was also more frequent in cholestatic patients (p = 0.042).

CONCLUSION

The common ABCB4 c.711A>T and ABCB11 p.A444V polymorphisms are more prevalent in adult patients with idiopathic cholestasis than in healthy controls and may therefore represent risk factors for the development of chronic cholestatic liver disease.

Formulation and delivery solutions for the next generation biotherapeutics

In 2018 I was appointed full professor of Pharmaceutical Biotechnology & Delivery at the Pharmaceutics division of the department of Pharmaceutical Sciences at Utrecht University, The Netherlands. In this contribution to the Orations - New Horizons of the Journal of Controlled Release I will introduce my research group (see also www.uu.nl/pharmaceutics) and will highlight my current and future research projects. In coming years the focus of my research will be on the administration of biotherapeutics, aiming to control their fate from the site of injection to the site of action. I will discuss issues related to formulation of biotherapeutics into nanomedicines (NMs), intracellular delivery of nucleic acids as well as protein therapeutics, and targeted delivery of biotherapeutics beyond the liver. In addition, I will provide a forward view on how current developments in the drug delivery and gene therapy field may result in sustainable and cost-effective dosing regimens for biotherapeutics.

Effect of CFTR correctors on the traffic and the function of intracellularly retained ABCB4 variants

BACKGROUND & AIM

ABCB4 is expressed at the canalicular membrane of hepatocytes. This ATP-binding cassette (ABC) transporter is responsible for the secretion of phosphatidylcholine into bile canaliculi. Missense genetic variations of ABCB4 are correlated with several rare cholestatic liver diseases, the most severe being progressive familial intrahepatic cholestasis type 3 (PFIC3). In a repurposing strategy to correct intracellularly retained ABCB4 variants, we tested 16 compounds previously validated as cystic fibrosis transmembrane conductance regulator (CFTR) correctors.

METHODS

The maturation, intracellular localization and activity of intracellularly retained ABCB4 variants were analyzed in cell models after treatment with CFTR correctors. In addition, in silico molecular docking calculations were performed to test the potential interaction of CFTR correctors with ABCB4.

RESULTS

We observed that the correctors C10, C13, and C17, as well as the combinations of C3 + C18 and C4 + C18, allowed the rescue of maturation and canalicular localization of four distinct traffic-defective ABCB4 variants. However, such treatments did not permit a rescue of the phosphatidylcholine secretion activity of these defective variants and were also inhibitory of the activity of wild type ABCB4. In silico molecular docking analyses suggest that these CFTR correctors might directly interact with transmembrane domains and/or ATP-binding sites of the transporter.

CONCLUSION

Our results illustrate the uncoupling between the traffic and the activity of ABCB4 because the same molecules can rescue the traffic of defective variants while they inhibit the secretion activity of the transporter. We expect that this study will help to design new pharmacological tools with potential clinical interest.

Synthetic human ABCB4 mRNA therapy rescues severe liver disease phenotype in a BALB/c.Abcb4-/- mouse model of PFIC3

BACKGROUND & AIMS

Progressive familial intrahepatic cholestasis type 3 (PFIC3) is a rare lethal autosomal recessive liver disorder caused by loss-of-function variations of the ABCB4 gene, encoding a phosphatidylcholine transporter (ABCB4/MDR3). Currently, no effective treatment exists for PFIC3 outside of liver transplantation.

METHODS

We have produced and screened chemically and genetically modified mRNA variants encoding human ABCB4 (hABCB4 mRNA) encapsulated in lipid nanoparticles (LNPs). We examined their pharmacological effects in a cell-based model and in a new in vivo mouse model resembling human PFIC3 as a result of homozygous disruption of the Abcb4 gene in fibrosis-susceptible BALB/c.Abcb4-/- mice.

RESULTS

We show that treatment with liver-targeted hABCB4 mRNA resulted in de novo expression of functional hABCB4 protein and restored phospholipid transport in cultured cells and in PFIC3 mouse livers. Importantly, repeated injections of the hABCB4 mRNA effectively rescued the severe disease phenotype in young Abcb4-/- mice, with rapid and dramatic normalisation of all clinically relevant parameters such as inflammation, ductular reaction, and liver fibrosis. Synthetic mRNA therapy also promoted favourable hepatocyte-driven liver regeneration to restore normal homeostasis, including liver weight, body weight, liver enzymes, and portal vein blood pressure.

CONCLUSIONS

Our data provide strong preclinical proof-of-concept for hABCB4 mRNA therapy as a potential treatment option for patients with PFIC3.

LAY SUMMARY

This report describes the development of an innovative mRNA therapy as a potential treatment for PFIC3, a devastating rare paediatric liver disease with no treatment options except liver transplantation. We show that administration of our mRNA construct completely rescues severe liver disease in a genetic model of PFIC3 in mice.

Clinical characteristics and genetic profiles of young and adult patients with cholestatic liver disease

BACKGROUND AND AIMS

heterozygous ABCB4, ABCB11 and ATP8B1 sequence variants were previously reported to be associated with low phospholipid-associated cholelithiasis, intrahepatic cholestasis of pregnancy, benign recurrent intrahepatic cholestasis and biliary lithiasis. The present study aimed to identify the presence of sequence variations in genes responsible for Mendelian liver disorders in patients with cholestatic liver disease.

METHODS

targeted massive parallel sequencing of a panel of genes involved in bile acid homeostasis was performed in 105 young and adult patients with cholestatic liver disease in our laboratory for molecular diagnosis. The effects of novel variants were evaluated using bioinformatics prediction tools and the Protter and Phyre2 software programs were used to create 2D, 3D topology protein modeling. Genotype-phenotype correlation was established according to molecular analysis and clinical records.

RESULTS

twenty novel heterozygous ABCB4 sequence variations, one heterozygous ABCB4 large intragenic deletion and only one novel missense variant in ABCB11 and ATP8B1 were identified. Interestingly, heterozygous and homozygous SLC4A2 missense variants were detected in patients with low phospholipid-associated cholelithiasis. Two patients harbored heterozygous GPBAR1 variants. Common variants such as homozygous ABCB11 p.Val444Ala and heterozygous ABCG8 p.Asp19His were also identified in 12 cases.

CONCLUSIONS

forty-eight variants were identified in five genes including ABCB4, ABCB11, ATP8B1, SLC4A2 and GPBAR1, twenty-five of which were novel. This study expands the phenotypic and mutational spectrum in genes involved in bile acid homeostasis and highlights the genetic and phenotypic heterogeneity in patients with inherited liver disorders.

Variants in ABCB4 (MDR3) across the spectrum of cholestatic liver diseases in adults

The ATP binding cassette subfamily B member 4 (ABCB4) gene on chromosome 7 encodes the ABCB4 protein (alias multidrug resistance protein 3 [MDR3]), a P-glycoprotein in the canalicular membrane of the hepatocytes that acts as a translocator of phospholipids into bile. Several variants in ABCB4 have been shown to cause ABCB4 deficiency, accounting for a disease spectrum ranging from progressive familial cholestasis type 3 to less severe conditions like low phospholipid-associated cholelithiasis, intrahepatic cholestasis of pregnancy or drug-induced liver injury. Furthermore, whole genome sequencing has shown that ABCB4 variants are associated with an increased incidence of gallstone disease, gallbladder and bile duct carcinoma, liver cirrhosis or elevated liver function tests. Diagnosis of ABCB4 deficiency-related diseases is based on clinical presentation, serum biomarkers, imaging techniques, liver histology and genetic testing. Nevertheless, the clinical presentation can vary widely and clear genotype-phenotype correlations are currently lacking. Ursodeoxycholic acid is the most commonly used medical treatment, but its efficacy has yet to be proven in large controlled clinical studies. Future pharmacological options may include stimulation/restoration of residual function by chaperones (e.g. 4-phenyl butyric acid, curcumin) or induction of ABCB4 transcription by FXR (farnesoid X receptor) agonists or PPARα (peroxisome proliferator-activated receptor-α)-ligands/fibrates. Orthotopic liver transplantation remains the last and often only therapeutic option in cirrhotic patients with end-stage liver disease or patients with intractable pruritus.

Familial intrahepatic cholestasis: New and wide perspectives

BACKGROUND

Progressive familial intrahepatic cholestasis (PFIC) includes autosomal recessive cholestatic rare diseases of childhood.

AIMS

To update the panel of single genes mutations involved in familial cholestasis.

METHODS

PubMed search for "familial intrahepatic cholestasis" alone as well as in combination with other key words was performed considering primarily original studies and meta-analyses.

RESULTS

PFIC1 involves ATP8B1 gene encoding for aminophospholipid flippase FIC1. PFIC2 includes ABCB11 gene, encoding for protein functioning as bile salt export pump. PFIC3 is due to mutations of ABCB4 gene responsible for the synthesis of class III multidrug resistance P-glycoprotein flippase. PFIC4 and PFIC5 involve tight junction protein-2 gene and NR1H4 gene encoding for farnesoid X receptor. Benign Intrahepatic Cholestasis, Intrahepatic Cholestasis of Pregnancy and Low-phospholipid-associated cholelithiasis involve the same genes and are characterized by intermittent attacks of cholestasis, no progression to cirrhosis, reversible pregnancy-specific cholestasis and cholelithiasis in young people. Blood and liver tissue levels of bile-excreted drugs can be influenced by the presence of mutations in PFIC genes, causing drug-induced cholestasis. Mutations in PFIC genes might increase the risk of liver cancer.

CONCLUSION

There is a high proportion of unexplained cholestasis potentially caused by specific genetic pathophysiologic pathways. The use of next generation sequencing and whole-exome sequencing could improve the diagnostic process in this setting.

A homozygous ABCB4 mutation causing an LPAC syndrome evolves into cholangiocarcinoma

Low phospholipid-associated cholelithiasis (LPAC) is characterized by the association of ABCB4 mutations and low biliary phospholipid concentration with symptomatic and recurring cholelithiasis. In the present study, we reported a case of a 63-year-old woman, who presented a biliary pain beginning at the age of 30, recurrent after cholecystectomy, along with "comet-tail shadows" revealed by ultrasonography thus, fulfilling the diagnosis of LPAC. This disease evolved into a cholangiocarcinoma. To understand the molecular basis of this phenotype, we performed the ABCB4 gene sequencing, followed by in silico analysis and Q-RT-PCR assay. The results displayed a homozygous missense sequence variation (c.140G > A, p.Arg47Gln), predicted as pathogenic according to MutPred. Accordingly, this gave rise to a decreased hepatic ABCB4 mRNA level and structural alterations of the mutated protein. Eventually, we reported, here, the first description of an ABCB4 missense mutation (p.Arg47Gln) at homozygous state in a Tunisian LPAC syndrome. An elucidation of its functional consequences was performed. Besides, this case suggests that the delayed diagnosis of LPAC syndrome and the lack of UDCA treatment may contribute in the development of complications, such as cholangiocarcinoma.

Cryptogenic cholestasis in young and adults: ATP8B1, ABCB11, ABCB4, and TJP2 gene variants analysis by high-throughput sequencing

BACKGROUND

Mutations in ATP-transporters ATPB81, ABCB11, and ABCB4 are responsible for progressive familial intrahepatic cholestasis (PFIC) 1, 2 and 3, and recently the gene for tight junction protein-2 (TJP2) has been linked to PFIC4.

AIM

As these four genes have been poorly studied in young people and adults, we investigated them in this context here.

METHODS

In patients with cryptogenic cholestasis, we analyzed the presence of mutations by high-throughput sequencing. Bioinformatics analyses were performed for mechanistic and functional predictions of their consequences on biomolecular interaction interfaces.

RESULTS

Of 108 patients, 48 whose cause of cholestasis was not established were submitted to molecular analysis. Pathogenic/likely pathogenic mutations were found in ten (21%) probands for 13 mutations: two in ATP8B 1, six in ABCB11, two in ABCB4, three in TJP2. We also identified seven variants of uncertain significance: two in ATP8B1, one in ABCB11, two in ABCB4 and two in TJP2. Finally, we identified 11 benign/likely benign variants. Patients with pathogenic/likely pathogenic mutations had higher levels of liver stiffness (measured by FibroScan^®) and bile acids, as well as higher rates of cholestatic histological features, compared to the patients without at least likely pathogenic mutations. The multivariate analysis showed that itching was the only independent factor associated with disease-causing mutations (OR 5.801, 95% CI 1.244-27.060, p = 0.025).

CONCLUSIONS

Mutations in the genes responsible for PFIC may be involved in both young and adults with cryptogenic cholestasis in a considerable number of cases, including in heterozygous status. Diagnosis should always be suspected, particularly in the presence of itching.

Phenotypic spectrum and diagnostic pitfalls of ABCB4 deficiency depending on age of onset

Genetic variants in the adenosine triphosphate-binding cassette subfamily B member 4 (ABCB4) gene, which encodes hepatocanalicular phosphatidylcholine floppase, can lead to different phenotypes, such as progressive familial intrahepatic cholestasis (PFIC) type 3, low phospholipid-associated cholelithiasis, and intrahepatic cholestasis of pregnancy. The aim of this multicenter project was to collect information on onset and progression of this entity in different age groups and to assess the relevance of this disease for the differential diagnosis of chronic liver disease. Clinical and laboratory data of 38 patients (17 males, 21 females, from 29 families) with homozygous or (compound) heterozygous ABCB4 mutations were retrospectively collected. For further analysis, patients were grouped according to the age at clinical diagnosis of ABCB4-associated liver disease into younger age (<18 years) or adult age (≥18 years). All 26 patients diagnosed in childhood presented with pruritus (median age 1 year). Hepatomegaly and splenomegaly were present in 85% and 96% of these patients, respectively, followed by jaundice (62%) and portal hypertension (69%). Initial symptoms preceded diagnosis by 1 year, and 13 patients received a liver transplant (median age 6.9 years). Of note, 9 patients were misdiagnosed as biliary atresia, Alagille syndrome, or PFIC type 1. In the 12 patients with diagnosis in adulthood, the clinical phenotype was generally less severe, including intrahepatic cholestasis of pregnancy, low phospholipid-associated cholelithiasis, or (non)cirrhotic PFIC3. Conclusion: ABCB4 deficiency with onset in younger patients caused a more severe PFIC type 3 phenotype with the need for liver transplantation in half the children. Patients with milder phenotypes are often not diagnosed before adulthood. One third of the children with PFIC type 3 were initially misdiagnosed, indicating the need for better diagnostic tools and medical education. (Hepatology Communications 2018;2:504-514).

Management options for cholestatic liver disease in children

Due to a peculiar age-dependent increased susceptibility, neonatal cholestasis affects the liver of approximately 1 in every 2500 term infants. A high index of suspicion is the key to an early diagnosis, and to implement timely, often life-saving treatments. Even when specific treatment is not available or curative, prompt medical management and optimization of nutrition are of paramount importance to survival and avoidance of complications. Areas covered: The present article will prominently focus on a series of newer diagnostic and therapeutic options of cholestasis in neonates and infants blended with consolidated established paradigms. The overview of strategies for the management reported here is based on a systematic literature search published in English using accessible databases (PubMed, MEDLINE) with the keywords biliary atresia, choleretics and neonatal cholestasis. References lists from retrieved articles were also reviewed. Expert commentary: A large number of uncommon and rare hepatobiliary disorders may present with cholestasis during the neonatal and infantile period. Potentially life-saving disease-specific pharmacological and surgical therapeutic approaches are currently available. Advances in hepatobiliary transport mechanisms have started clarifying fundamental aspects of inherited and acquired cholestasis, laying the foundation for the development of possibly more effective specific therapies.

Chronic Pruritus in an 18-Month-Old Male Infant Due to Anicteric Cholestasis

An 18-month-old male infant was referred to us with pruritus from 6 months of age. He was being managed as atopic eczema with emollients and antihistamines without any response to treatment. On examination, he was found to have extensive scratch marks, mild hepatomegaly and no icterus. Blood investigations were suggestive of anicteric cholestatic liver disease. Liver biopsy was suggestive of progressive familial intrahepatic cholestasis type 3. He showed symptomatic improvement after starting ursodeoxycholic acid and fat-soluble vitamins and is under follow up.

The characteristics of activated portal fibroblasts/myofibroblasts in liver fibrosis

Liver fibrosis results from chronic injury of hepatocytes and activation of Collagen Type I producing myofibroblasts that produce fibrous scar in liver fibrosis. Myofibroblasts are not present in the normal liver but rapidly appear early in experimental and clinical liver injury. The origin of the myofibroblast in liver fibrosis is still unresolved. The possibilities include activation of liver resident cells including portal fibroblasts, hepatic stellate cells, mesenchymal progenitor cells, and fibrocytes recruited from the bone marrow. It is considered that hepatic stellate cells and portal fibroblasts are the major source of hepatic myofibroblasts. In fact, the origin of myofibroblasts differs significantly for chronic liver diseases of different etiologies, such as cholestatic liver disease or hepatotoxic liver disease. Depending on etiology of hepatic injury, the fibrogenic foci might initiate within the hepatic lobule as seen in chronic hepatitis, or primarily affect the portal areas as in most biliary diseases. It has been suggested that activated portal fibroblasts/myofibroblasts work as "myofibroblasts for cholangiocytes" while hepatic stellate cells work as "myofibroblast for hepatocytes". This review will focus on our current understanding of the activated portal fibroblasts/myofibroblasts in cholestatic liver fibrosis.

A functional classification of ABCB4 variations causing progressive familial intrahepatic cholestasis type 3

Progressive familial intrahepatic cholestasis type 3 is caused by biallelic variations of ABCB4, most often (≥70%) missense. In this study, we examined the effects of 12 missense variations identified in progressive familial intrahepatic cholestasis type 3 patients. We classified these variations on the basis of the defects thus identified and explored potential rescue of trafficking-defective mutants by pharmacological means. Variations were reproduced in the ABCB4 complementary DNA and the mutants, thus obtained, expressed in HepG2 and HEK293 cells. Three mutants were either fully (I541F and L556R) or largely (Q855L) retained in the endoplasmic reticulum, in an immature form. Rescue of the defect, i.e., increase in the mature form at the bile canaliculi, was obtained by cell treatments with cyclosporin A or C and, to a lesser extent, B, D, or H. Five mutations with little or no effect on ABCB4 expression at the bile canaliculi caused a decrease (F357L, T775M, and G954S) or almost absence (S346I and P726L) of phosphatidylcholine secretion. Two mutants (T424A and N510S) were normally processed and expressed at the bile canaliculi, but their stability was reduced. We found no defect of the T175A mutant or of R652G, previously described as a polymorphism. In patients, the most severe phenotypes appreciated by the duration of transplant-free survival were caused by ABCB4 variants that were markedly retained in the endoplasmic reticulum and expressed in a homozygous status.

CONCLUSION

ABCB4 variations can be classified as follows: nonsense variations (I) and, on the basis of current findings, missense variations that primarily affect the maturation (II), activity (III), or stability (IV) of the protein or have no detectable effect (V); this classification provides a strong basis for the development of genotype-based therapies.

Molecular characterization of exons 6, 8 and 9 of ABCB4 gene in children with Progressive Familial Intrahepatic Cholestasis type 3

AIM OF WORK

To estimate the frequency of mutations involving exons 6, 8 and 9 of Adenosine triphosphate-binding cassette, subfamily B, member 4 (ABCB4) gene among children with progressive intrahepatic cholestasis with high γ-GT activity (PFIC3).

SUBJECTS AND METHODS

Cross sectional study was conducted on 30 children with PFIC3. Genotyping was performed by sequencing analysis of exons 6, 8 and exon 9 of ABCB4 gene.

RESULTS

Heterozygous synonymous polymorphic variant was detected in exon 6 (rs 1202283) and in exon 8 (rs 2109505). No mutations in studied exons were detected.

CONCLUSION

Exons 6, 8 and 9 mutations of ABCB4 gene are not common among Egyptian children with PFIC3.

ABCB4 mutations in adult patients with cholestatic liver disease: impact and phenotypic expression

BACKGROUND

The ABCB4 gene encodes the MDR3 protein. Mutations of this gene cause progressive familial intrahepatic cholestasis type 3 (PFIC3) in children, but their clinical relevance in adults remains ill defined. The study of a well-characterized adult patient series may contribute to refining the genetic data regarding cholangiopathies of unknown origin. Our aim was to evaluate the impact of ABCB4 mutations on clinical expression of cholestasis in adult patients.

METHODS

We consecutively evaluated 2602 subjects with hepatobiliary disease. Biochemical evidence of a chronic cholestatic profile (CCP) with elevated serum gamma-glutamyltransferase activity or diagnosis of intrahepatic cholestasis of pregnancy (ICP) and juvenile cholelithiasis (JC) were inclusion criteria. The personal/family history of additional cholestatic liver disease (PFH-CLD), which includes ICP, JC, or hormone-induced cholestasis, was investigated. Mutation screening of ABCB4 was carried out in 90 patients with idiopathic chronic cholestasis (ICC), primary biliary cirrhosis (PBC), primary sclerosing cholangitis (PSC), ICP, and JC.

RESULTS

Eighty patients had CCP. PSC and ICC patients with PFH-CLD had earlier onset of disease than those without it (p = 0.003 and p = 0.023, respectively). The mutation frequency ranged from 50% (ICP, JC) to 17.6% (PBC). Among CCP patients, presence or absence of PFH-CLD was associated with ABCB4 mutations in 26.8 vs 5.1% (p = 0.013), respectively; in the subset of ICC and PSC patients, the corresponding figures were 44.4 vs 0% (p = 0.012) and 28.6 vs 8.7% (p = 0.173).

CONCLUSIONS

Cholangiopathies attributable to highly penetrant ABCB4 mutant alleles are identifiable in a substantial proportion of adults that generally have PFH-CLD. In PSC and ICC phenotypes, patients with MDR3 deficiency have early onset of disease.

Heterozygous ABCB4 mutations in children with cholestatic liver disease

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.

Analysis of mutations of MDR3 exons 9 and 23 in infants with parenteral nutrition-associated cholestasis

The aim of this study was to investigate mutations of multidrug resistance 3 (MDR3) exons 9 and 23 in infants with parenteral nutrition-associated cholestasis (PNAC). A total of 41 infants with PNAC were enrolled in the study. Genomic DNA was extracted from the peripheral venous blood leukocytes of each patient and MDR3 exons 9 and 23 were amplified by polymerase chain reaction. One patient was identified who carried a frameshift mutation in MDR3 exon 23 (C.2793) that was caused by the insertion of a single adenine residue, while mutations were not found in MDR3 exon 23 in the other 40 patients. The clinical features of the patient with the MDR3 exon 23 frameshift mutation included high serum γ-glutamyl transferase levels, the absence of biliary dilatation and deformity in magnetic resonance cholangiopancreatography, and abnormal electrical capacitance tomography imaging of the liver. No mutations in MDR3 exon 9 were identified in any of the patients. All 41 PNAC patients recovered following oral ursodeoxycholic acid treatment. The C.2793 frameshift mutation in MDR3 exon 23 is potentially associated with the development of PNAC in infants.

Liver biopsy in children: position paper of the ESPGHAN Hepatology Committee

Liver biopsy (LB) is still the criterion standard procedure for obtaining liver tissue for histopathological examination and a valuable tool in the diagnosis, prognosis, and management of many parenchymal liver diseases. The aim of this position paper is to summarise the present practice of paediatric LB and make recommendations about its performance. Although histological evaluation of the liver is important in assessing prognosis and exploring treatment, noninvasive techniques (ie, imaging, laboratory markers) may replace use of liver histology. The indications for LB are changing as present knowledge of aetiologies, pathomechanism, and therapeutic options in paediatric liver disease is evolving. Adult and paediatric literature was reviewed to assess the existing clinical practice of LB with focus on the technique, indications, risk of complications, and contraindications in paediatrics. This position paper presents types of LB, indications, complications, contraindications, and an essential checklist for paediatric LB.

Novel mutation in a Chinese patient with progressive familial intrahepatic cholestasis type 3

Genotyping is conclusive for the diagnosis of progressive familial intrahepatic cholestasis type 3 (PFIC3). Here we report a Chinese patient of PFIC3 with compound mutations in the ABCB4 gene. Liver biopsy was performed on a 17-year-old male patient with intrahepatic cholestasis of unknown etiology. Liver histology findings are indicative of intrahepatic cholestasis with extensive fibrosis. Genotyping revealed c.175C>T (p.L59L) mutation in exon 4, c.504C>T (p.N168N) mutation in exon 6, c.711A>T (p.I237I) mutation in exon 8, c.874A>T (p.K292X) in exon 9 and a novel mutation, c.1804G>T (p.G602W) in exon 15. Based on these findings, the patient was diagnosed with PFIC3. The novel mutation p.G602W in exon 15 was predicted as probably damaging by PolyPhen-2 with a score of 0.986 (sensitivity: 0.54; specificity: 0.94) and was predicted to affect protein function with a SIFT score of 0.01.

Functional analysis of ABCB4 mutations relates clinical outcomes of progressive familial intrahepatic cholestasis type 3 to the degree of MDR3 floppase activity

OBJECTIVE

Progressive familial intrahepatic cholestasis type 3 (PFIC3) is a potentially lethal autosomal recessive liver disease associated with mutations in ABCB4, the gene encoding the canalicular translocator of phosphatidylcholine MDR3. While some affected children benefit from ursodeoxycholic acid (UDCA) therapy, others evolve to end-stage liver disease. We aimed to evaluate whether these different outcomes are related to the impact of ABCB4 mutations.

DESIGN

Six children with PFIC3 were investigated by sequencing of ABCB4 exons and flanking intron-exon boundaries and by immunohistochemistry. ABCB4 missense mutations were phenotyped in vitro by assessing their effects on MDR3 expression, subcellular localisation, and phosphatidylcholine-translocating activity. The resulting data were contrasted with the clinical outcomes.

RESULTS

Eight distinct ABCB4 mutations were identified: one nonsense, one splicing and six missense mutations, four of which (G68R, T201M, P479L, D459H) affected MDR3 expression level. G68R and D459H also led to retention of the protein in endoplasmic reticulum. Phosphatidylcholine efflux assays indicated that T201M, P479L, S978P and E1118K mutations impaired MDR3 activity to variable degrees. Three children with mutations that caused a total loss of MDR3 expression/function manifested progressive liver disease refractory to UDCA treatment. This was also the case in a patient carrying two different mutations that, in combination, resulted in a 90% reduction in total MDR3 activity. A favourable response to UDCA was achieved in two patients with estimated MDR3 activities of 50% and 33%, respectively.

CONCLUSIONS

These data provide experimental evidence of the correlation between the degree of MDR3 floppase activity and the clinical outcomes of PFIC3.

ABCB4: Insights from pathobiology into therapy

Adenosine triphosphate (ATP)-binding cassette, sub-family B, member 4 (ABCB4), also called multidrug resistance 3 (MDR3), is a member of the ATP-binding cassette transporter superfamily, which is localized at the canalicular membrane of hepatocytes, and mediates the translocation of phosphatidylcholine into bile. Phosphatidylcholine secretion is crucial to ensure solubilization of cholesterol into mixed micelles and to prevent bile acid toxicity towards hepatobiliary epithelia. Genetic defects of ABCB4 may cause progressive familial intrahepatic cholestasis type 3 (PFIC3), a rare autosomic recessive disease occurring early in childhood that may be lethal in the absence of liver transplantation, and other cholestatic or cholelithiasic diseases in heterozygous adults. Development of therapies for these conditions requires understanding of the biology of this transporter and how gene variations may cause disease. This review focuses on our current knowledge on the regulation of ABCB4 expression, trafficking and function, and presents recent advances in fundamental research with promising therapeutic perspectives.

Correlation between mutation of MDR3 gene exon 6 and parenteral nutrition-associated cholestasis of preterm infants

The aim of this study was to investigate the association between the mutation of multidrug resistance 3 (MDR3) exon 6 and parenteral nutrition-associated cholestasis (PNAC) in preterm infants. A total of 41 preterm infants with PNAC formed the experimental group, and 56 preterm infants receiving total parenteral nutrition (TPN) for >14 days but without cholestasis formed the control group. Genomic DNA was extracted from peripheral venous blood leukocytes. Polymerase chain reaction was used to amplify exon 6 of the MDR3 gene. The target band of MDR3 gene exon 6 was identified in all blood samples from all cases. We identified five cases with C. 504 C>T heterozygous mutations of exon 6 of the MDR3 gene and 14 cases with C. 504 C>T homozygous mutations in the experimental group. In the control group, we identified seven cases with the C. 504 C>T homozygous mutation and six cases with the C. 504 C>T heterozygous mutation. The distribution of the T/C allele frequency of C. 504 in exon 6 of the MDR3 gene between the experimental group and control group was statistically significant (P<0.05). Further analysis revealed the odds ratio of the T/C allele frequency of the C. 504 mutation in exon 6 of the MDR3 gene between the experimental group and control group to be 0.316. Point mutation C. 485 T>A was detected in one case in the experimental group. The C. 504 C>T and C. 485 T>A MDR3 mutations in exon 6 are possibly responsible for the development of PNAC in infants. C. 504 C>T may not be the only risk factor of neonatal PNAC. In order to further confirm the association between exon 6 of the MDR3 gene and PNAC, a large-sample multicenter study should be carried out.

Phosphorylation of ABCB4 impacts its function: insights from disease-causing mutations

The ABCB4 transporter mediates phosphatidylcholine (PC) secretion at the canalicular membrane of hepatocytes and its genetic defects cause biliary diseases. Whereas ABCB4 shares high sequence identity with the multidrug transporter, ABCB1, its N-terminal domain is poorly conserved, leading us to hypothesize a functional specificity of this domain. A database of ABCB4 genotyping in a large series of patients was screened for variations altering residues of the N-terminal domain. Identified variants were then expressed in cell models to investigate their biological consequences. Two missense variations, T34M and R47G, were identified in patients with low-phospholipid-associated cholelithiasis or intrahepatic cholestasis of pregnancy. The T34M and R47G mutated proteins showed no or minor defect, respectively, in maturation and targeting to the apical membrane, in polarized Madin-Darby Canine Kidney and HepG2 cells, whereas their stability was similar to that of wild-type (WT) ABCB4. By contrast, the PC secretion activity of both mutants was markedly decreased. In silico analysis indicated that the identified variants were likely to affect ABCB4 phosphorylation. Mass spectrometry analyses confirmed that the N-terminal domain of WT ABCB4 could undergo phosphorylation in vitro and revealed that the T34M and R47G mutations impaired such phosphorylation. ABCB4-mediated PC secretion was also increased by pharmacological activation of protein kinases A or C and decreased by inhibition of these kinases. Furthermore, secretion activity of the T34M and R47G mutants was less responsive than that of WT ABCB4 to protein kinase modulators.

CONCLUSION

We identified disease-associated variants of ABCB4 involved in the phosphorylation of its N-terminal domain and leading to decreased PC secretion. Our results also indicate that ABCB4 activity is regulated by phosphorylation, in particular, of N-terminal residues.

Genetic diseases that predispose to early liver cirrhosis

Inherited liver diseases are a group of metabolic and genetic defects that typically cause early chronic liver involvement. Most are due to a defect of an enzyme/transport protein that alters a metabolic pathway and exerts a pathogenic role mainly in the liver. The prevalence is variable, but most are rare pathologies. We review the pathophysiology of such diseases and the diagnostic contribution of laboratory tests, focusing on the role of molecular genetics. In fact, thanks to recent advances in genetics, molecular analysis permits early and specific diagnosis for most disorders and helps to reduce the invasive approach of liver biopsy.

Molecular mechanistic explanation for the spectrum of cholestatic disease caused by the S320F variant of ABCB4

ABCB4 flops phosphatidylcholine into the bile canaliculus to protect the biliary tree from the detergent activity of bile salts. Homozygous-null ABCB4 mutations cause the childhood liver disease, progressive familial intrahepatic cholestasis, but cause and effect is less clear, with many missense mutations linked to less severe cholestatic diseases. ABCB4(S320F), in particular, is described in 13 patients, including in heterozygosity with ABCB4(A286V), ABCB4(A953D), and null mutants, whose symptoms cover the spectrum of cholestatic disease. We sought to define the impact of these mutations on the floppase, explain the link with multiple conditions at the molecular level, and investigate the potential for reversal. ABCB4(S320F), ABCB4(A286V), and ABCB4(A953D) expression was engineered in naïve cultured cells. Floppase expression, localization, and activity were measured by western blot, confocal microscopy, and lipid transport assays, respectively. ABCB4(S320F) was fully active for floppase activity but expression at the plasma membrane was reduced to 50%. ABCB4(A286V) expressed and trafficked efficiently but could not flop lipid, and ABCB4(A953D) expressed poorly and was impaired in floppase activity. Proteasome inhibition stabilized nascent ABCB4(S320F) and ABCB4(A953D) but did not improve plasma membrane localization. Cyclosporin-A improved plasma membrane localization of both ABCB4(S320F) and ABCB4(A953D), but inhibited floppase activity.

CONCLUSION

The level of ABCB4 functionality correlates with, and is the primary determinant of, cholestatic disease severity in these patients. ABCB4(S320F) homozygosity, with half the normal level of ABCB4, is the tipping point between more benign and potentially fatal cholestasis and makes these patients more acutely sensitive to environmental effects. Cyclosporin-A increased expression of ABCB4(S320F) and ABCB4(A953D), suggesting that chemical chaperones could be exploited for therapeutic benefit to usher in a new era of personalized medicine for patients with ABCB4-dependent cholestatic disease.

Management of adults with paediatric-onset chronic liver disease: strategic issues for transition care

Advances in the management of children with chronic liver disease have enabled many to survive into adulthood with or without their native livers, so that the most common of these conditions are becoming increasingly common in adult hepatology practice. Because the aetiologies of chronic liver disease in children may vary significantly from those in adulthood, adults with paediatric-onset chronic liver disease may often present with clinical manifestations unfamiliar to their adulthood physician. Transition of medical care to adult practice requires that the adulthood medical staff (primary physicians and subspecialists) have a comprehensive knowledge of childhood liver disease and their implications, and of the differences in caring for these patients. Pending still unavailable Scientific Society guidelines, this article examines causes, presentation modes, evaluation, management, and complications of the main paediatric-onset chronic liver diseases, and discusses key issues to aid in planning a program of transition from paediatric to adult patients.

Two ABCB4 point mutations of strategic NBD-motifs do not prevent protein targeting to the plasma membrane but promote MDR3 dysfunction

The ABCB4 gene encodes for MDR3, a protein that translocates phosphatidylcholine from the inner to the outer leaflet of the hepatocanalicular membrane; its deficiency favors the formation of 'toxic bile'. Several forms of hepatobiliary diseases have been associated with ABCB4 mutations, but the detrimental effects of most mutations on the encoded protein needs to be clarified. Among subjects with cholangiopathies who were screened for mutations in ABCB4 by direct sequencing, we identified the new mutation p.(L481R) in three brothers. According to our model of tertiary structure, this mutation affects the Q-loop, whereas the p.(Y403H) mutation, that we already described in two other families, involves the A-loop. This study was aimed at analyzing the functional relevance of these two ABCB4 mutations: MDR3 expression and lipid content in the culture supernatant were evaluated in cell lines stably transfected with the ABCB4 wild-type clone and corresponding mutants. No differences of expression were observed between wild-type and mutant gene products. Instead, both mutations caused a reduction of phosphatidylcholine secretion compared with the wild-type transfected cell lines. On the contrary, cholesterol (Chol) release, after 1 and 3 mM sodium taurocholate stimulation, was higher in the mutant-transfected cell lines than that in the wild-type and was particularly enhanced in cells transfected with the p.Y403H-construct.In summary, our data show that both mutations do not seem to affect protein expression, but are able to reduce the efflux of phosphatidylcholine associated with increase of Chol, thereby promoting the formation of toxic bile.

Pediatric Cholestatic Disorders: Approach to Pathologic Diagnosis

This article addresses select liver diseases that are commonly seen in the pediatric group and pose diagnostic challenges in practice. The key genetic/molecular abnormalities, clinical features, histopathologic findings, diagnostic modalities, differential diagnoses, and possible pitfalls in diagnosis are discussed in detail. Although recent advances in understanding the pathophysiology of bile synthesis and transport along with advances in molecular genetics have allowed a better characterization of many of these liver diseases, significant overlap in the histopathologic features of many of these disorders still leads to diagnostic challenges for the pathologist.

Fatty liver disease and hypertransaminasemia hiding the association of clinically silent Duchenne muscular dystrophy and hereditary fructose intolerance

We report a case with the association of well self-compensated hereditary fructose intolerance and still poorly symptomatic Duchenne type muscular dystrophy. This case illustrates the problems of a correct diagnosis in sub-clinical patients presenting with “cryptogenic” hypertransaminasemia.

Chinese children with chronic intrahepatic cholestasis and high γ-glutamyl transpeptidase: clinical features and association with ABCB4 mutations

OBJECTIVE

The aims of the present study was to study the significance of ABCB4 mutations in mainland Chinese children with chronic intrahepatic cholestasis and to correlate genetic findings with clinical features and response to ursodeoxycholic acid (UDCA) therapy.

METHODS

Thirteen patients with chronic intrahepatic cholestasis and elevated serum γ-glutamyl transpeptidase activity of unknown cause were enrolled in a single pediatric center. All of the encoding exons and flanking areas of ABCB4 were sequenced. Available liver biopsy specimens were immunostained for multidrug resistance protein 3. The clinical features, biochemical parameters, and responses to therapy were compared with patients with or without ABCB4 mutation(s).

RESULTS

Six different ABCB4 mutations were identified in 3 patients; each patient was a compound heterozygote. Apart from c.139C>T (p.R47X), all were novel, including c.344+2_+3insT, c.1376A>G (p.D459G), c.1745G>A (p.R582Q), c.2077_2078delC (p.P693HfsX698), and c.3825_3826delA (p.M1276WfsX1308). Absent or reduced multidrug resistance protein 3 canalicular immunostaining was demonstrated in patients with ABCB4 mutations. Serum total bile acid levels were higher in patients with ABCB4 mutations than in patients without ABCB4 mutations (352.5 ± 97.0 vs 55.9 ± 50.4 μmol/L, P = 7.32E-05). There was no difference in other biochemical parameters between patients with and without ABCB4 mutations. After oral UDCA administration in 3 patients with ABCB4 mutations, pruritus disappeared, growth improved, spleen size decreased, and platelet counts increased. In the 10 patients without ABCB4 mutations, an inconsistent response to UDCA therapy was observed.

CONCLUSIONS

In mainland Chinese children, some cases of chronic intrahepatic cholestasis with high γ-glutamyl transpeptidase could be attributed to ABCB4 mutations. UDCA administration partially improved clinical symptoms and liver function.

First description of ABCB4 gene deletions in familial low phospholipid-associated cholelithiasis and oral contraceptives-induced cholestasis

The wide clinical spectrum of the ABCB4 gene (ATP-binding cassette subfamily B member 4) deficiency syndromes in humans includes low phospholipid-associated cholelithiasis (LPAC), intrahepatic cholestasis of pregnancy (ICP), oral contraceptives-induced cholestasis (CIC), and progressive familial intrahepatic cholestasis type 3 (PFIC3). No ABCB4 mutations are found in a significant proportion of patients with these syndromes. In the present study, 102 unrelated adult patients with LPAC (43 patients) or CIC/ICP (59 patients) were screened for ABCB4 mutations using DNA sequencing. Heterozygous ABCB4 point or short insertion/deletion mutations were found in 37% (16/43) of the LPAC patients and in 27% (16/59) of the ICP/CIC patients. High-resolution gene dosage methodologies were used in the 70 negative patients. Here, we describe for the first time ABCB4 partial or complete heterozygous deletions in 7% (3/43) of the LPAC patients, and in 2% (1/59) of the ICP/CIC patients. Our observations urge to systematically test patients with LPAC, ICP/CIC, and also children with PFIC3 for the presence of ABCB4 deletions using molecular tools allowing detection of gross rearrangements. In clinical practice, a comprehensive ABCB4 alteration-screening algorithm will permit the use of ABCB4 genotyping to confirm the diagnosis of LPAC or ICP/CIC, and allow familial testing. An early diagnosis of these biliary diseases may be beneficial because of the preventive effect of ursodeoxycholic acid on biliary complications. Further comparative studies of patients with well-characterized genotypes (including deletions) and phenotypes will help determine whether ABCB4 mutation types influence clinical outcomes.