Heterozygous non-sense mutation of the MDR3 gene in familial intrahepatic cholestasis of pregnancy

Genetics of liver disease: From pathophysiology to clinical practice

Paralleling the first 30 years of the Journal of Hepatology we have witnessed huge advances in our understanding of liver disease and physiology. Genetic advances have played no small part in that. Initial studies in the 1970s and 1980s identified the strong major histocompatibility complex associations in autoimmune liver diseases. During the 1990 s, developments in genomic technologies drove the identification of genes responsible for Mendelian liver diseases. Over the last decade, genome-wide association studies have allowed for the dissection of the genetic susceptibility to complex liver disorders, in which also environmental co-factors play important roles. Findings have allowed the identification and elaboration of pathophysiological processes, have indicated the need for reclassification of liver diseases and have already pointed to new disease treatments. In the immediate future genetics will allow further stratification of liver diseases and contribute to personalized medicine. Challenges exist with regard to clinical implementation of rapidly developing technologies and interpretation of the wealth of accumulating genetic data. The historical perspective of genetics in liver diseases illustrates the opportunities for future research and clinical care of our patients.

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.

Variations of ABCB4 and ABCB11 genes are associated with primary intrahepatic stones

Variations of the ABCB4 and ABCB11 genes affect the composition of bile and are associated with cholestasis and cholelithiasis. However, their roles in the formation of primary intrahepatic stones (PIS) remains to be elucidated. The aim of the present study was to determine whether there is an association between PIS and variations in these genes. Exon sequencing was performed in order to analyze the ABCB4 and ABCB11 genes of 176 patients with PIS and 178 healthy subjects. One mutation in ABCB4 (no. 69233, G>A) and two other mutations in ABCB11, reference single nucleotide polymorphism (rs)118109635 and rs497692, were identified in association with PIS (P<0.001, P=0.04 and P=0.02, respectively). A synonymous mutation at no. 69233 G>A was detected in exon 26 of ABCB4 in 23 heterozygous patients with PIS. This mutation was not detected in healthy individuals or in the Single Nucleotide Polymorphism Database. No. 69233 G>A in ABCB4 was not associated with altered protein expression but with a reduced rate of PIS recurrence (P=0.01). The missense mutation rs118109635 was located on exon 21 of ABCB11 and was associated with the increased expression of ABCB11 protein (P=0.032) as well as altered bile salt export pump function. Another synonymous mutation, rs497692 in exon 24 was reported to decrease ABCB11 protein expression (P=0.001). In addition, the mutations of ABCB11 were associated with preoperative jaundice (P<0.001 and P=0.03, respectively). Consistently decreased levels of ABCB11 protein were associated with recurrent episodes of cholangitis (P=0.006) and preoperative jaundice (P=0.015). By contrast, ABCB4 expression was not found to be associated with clinical manifestations of PIS.

Effect of drug transporter pharmacogenetics on cholestasis

INTRODUCTION

The liver is the central place for the metabolism of drugs and other xenobiotics. In the liver cell, oxidation and conjugation of compounds take place, and at the same time, bile formation helps in extrusion of these compounds via the biliary route. A large number of transporters are responsible for drug uptake into the liver cell and excretion into bile or efflux to the sinusoidal blood.

AREAS COVERED

Genetic variants of these transporters and their transactivators contribute to changes in drug handling and are also responsible for cholestatic syndromes of different severity. This review summarizes the current knowledge regarding the influence of these genetic changes. The review covers progressive hereditary cholestatic syndromes as well as recurrent or transient cholestatic syndromes such as drug-induced liver injury, intrahepatic cholestasis of pregnancy, and benign recurrent intrahepatic cholestasis.

EXPERT OPINION

Polymorphisms in transporter genes are frequent. For clinically relevant cholestatic syndromes, it often requires a combination of genetic variants or acquired triggers such as pregnancy or drug treatment. In combination with other pathogenetic aspects, genetic variants in drug transporters may contribute to our understanding of not only cholestatic diseases such as primary sclerosing cholangitis or primary biliary cirrhosis, but also the natural course of chronic liver disease in general.

Intrahepatic cholestasis of pregnancy

Intrahepatic cholestasis of pregnancy is the most common pregnancy-specific liver disease that typically presents in the third trimester. The clinical features are maternal pruritus in the absence of a rash and deranged liver function tests, including raised serum bile acids. Intrahepatic cholestasis of pregnancy is associated with an increased risk of adverse perinatal outcomes, including spontaneous preterm delivery, meconium staining of the amniotic fluid, and stillbirth. It is commonly treated with ursodeoxycholic acid. There is accumulating evidence to suggest that intrahepatic cholestasis of pregnancy has a lasting influence on both maternal and fetal health. We review the etiology, diagnosis, and management of this intriguing condition.

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.

HELLP syndrome preceded by intrahepatic cholestasis of pregnancy: one serious itch

We present four women with seven ongoing pregnancies. Five pregnancies were complicated by intrahepatic cholestasis of pregnancy (ICP) and severe haemolysis, elevated liver enzymes and low platelets (HELLP) syndrome with uncommon maternal morbidity. The combination of ICP and HELLP syndrome has not previously been reported. Awareness is warranted to accurately identify this combination of pregnancy-specific diseases with severe maternal morbidity.

The etiology of intrahepatic cholestasis of pregnancy: towards solving a monkey puzzle

Clinical and epidemiological findings implicate genetic predisposition and the effects of elevated steroids in pregnancy in the pathogenesis of intrahepatic cholestasis of pregnancy. To date, a number of studies have identified polymorphisms encoding biliary canalicular transporters, including those encoded by ABCB4 and ABCB11, which are associated with intrahepatic cholestasis of pregnancy. Questions remain regarding divergent findings between populations and the relative contributions of these polymorphisms. In a large study of Western European women with intrahepatic cholestasis of pregnancy, Dixon et al. (this issue) provide further insights into the genetics of this cholestatic syndrome, which contribute to ongoing evaluation of cholestasis generally.

A comprehensive analysis of common genetic variation around six candidate loci for intrahepatic cholestasis of pregnancy

OBJECTIVES

Intrahepatic cholestasis of pregnancy (ICP) has a complex etiology with a significant genetic component. Heterozygous mutations of canalicular transporters occur in a subset of ICP cases and a population susceptibility allele (p.444A) has been identified in ABCB11. We sought to expand our knowledge of the detailed genetic contribution to ICP by investigation of common variation around candidate loci with biological plausibility for a role in ICP (ABCB4, ABCB11, ABCC2, ATP8B1, NR1H4, and FGF19).

METHODS

ICP patients (n=563) of white western European origin and controls (n=642) were analyzed in a case-control design. Single-nucleotide polymorphism (SNP) markers (n=83) were selected from the HapMap data set (Tagger, Haploview 4.1 (build 22)). Genotyping was performed by allelic discrimination assay on a robotic platform. Following quality control, SNP data were analyzed by Armitage's trend test.

RESULTS

Cochran-Armitage trend testing identified six SNPs in ABCB11 together with six SNPs in ABCB4 that showed significant evidence of association. The minimum Bonferroni corrected P value for trend testing ABCB11 was 5.81×10(-4) (rs3815676) and for ABCB4 it was 4.6×10(-7)(rs2109505). Conditional analysis of the two clusters of association signals suggested a single signal in ABCB4 but evidence for two independent signals in ABCB11. To confirm these findings, a second study was performed in a further 227 cases, which confirmed and strengthened the original findings.

CONCLUSIONS

Our analysis of a large cohort of ICP cases has identified a key role for common variation around the ABCB4 and ABCB11 loci, identified the core associations, and expanded our knowledge of ICP susceptibility.

Prevalence of low phospholipid-associated cholelithiasis in young female patients

BACKGROUND AND AIMS

We evaluated the prevalence of low phospholipid-associated cholelithiasis, a specific form of cholelithiasis associated with at least 2 of the 3 following criteria: first symptoms before the age of 40; intrahepatic comet tail artefacts, sludge or microlithiasis on ultrasound imaging; and recurrence of symptoms after cholecystectomy.

METHODS

We prospectively studied the cases of 60 consecutive female patients under 30 with symptomatic cholelithiasis.

RESULTS

A diagnosis of low phospholipid-associated cholelithiasis was made in 14/60 patients (23%). The molecular analysis showed ABCB4 (n=4) and ABCB11 (n=4) gene mutations. Low phospholipid-associated cholelithiasis was frequently observed in non-overweight patients [13/27 (48%)], was present in most patients whose biliary symptoms occurred before the age of 18 [7/10 (70%)] and was often associated with cholangitis or acute pancreatitis [9/14 (64%), p<0.05] while "common" cholelithiasis was mainly associated with cholecystitis [16/46 (35%), p<0.05].

CONCLUSION

Nearly one quarter of the female patients under the age of 30 admitted for symptomatic cholelithiasis had low phospholipid-associated cholelithiasis; particularly if body weight was normal, the symptoms began before the age of 18 or in the presence of severe biliary complications.

Intrahepatic cholestasis of pregnancy and associated hepatobiliary disease: a population-based cohort study

Intrahepatic cholestasis of pregnancy (ICP) is the most common liver disease in pregnancy. We aimed to estimate the risk of developing hepatobiliary disease in women with ICP and the odds of developing ICP in women with prevalent hepatobiliary disease. We analyzed data of women with births between 1973 and 2009 and registered in the Swedish Medical Birth Register. By linkage with the Swedish Patient Register, we identified 11,388 women with ICP who were matched to 113,893 women without this diagnosis. Diagnoses of preexisting or later hepatobiliary disease were obtained from the Patient Register. Main outcome measures were hazard ratios (HRs) for later hepatobiliary disease in women with ICP and odds ratios (ORs) for developing ICP in preexisting hepatobiliary disease. Risk estimates were calculated through Cox and logistic regression analyses. Women with ICP were more often diagnosed with later hepatobiliary disease (HR 2.62; 95% confidence interval [CI] 2.47-2.77; increment at 1% per year), hepatitis C or chronic hepatitis (HR 4.16; 3.14-5.51 and 5.96; 3.43-10.33, respectively), fibrosis/cirrhosis (HR 5.11; 3.29-7.96), gallstone disease or cholangitis (HR 2.72; 2.55-2.91, and 4.22; 3.13-5.69, respectively) as compared to women without ICP (P < 0.001 for all HRs). Later ICP was more common in women with prepregnancy hepatitis C (OR 5.76; 1.30-25.44; P = 0.021), chronic hepatitis (OR 8.66; 1.05-71.48; P = 0.045), and gallstone disease (OR 3.29; 2.02-5.36; P < 0.0001).

CONCLUSION

Women with ICP have substantially increased risk for later hepatobiliary disease. Beyond gallstone-related morbidity we found a strong positive association between ICP and hepatitis C both before and after ICP diagnosis. Thus, we advocate testing for hepatitis C in women with ICP, in particular, since this potentially life-threatening infection can be treated successfully in the majority of patients.

Genotype-phenotype relationships in the low-phospholipid-associated cholelithiasis syndrome: a study of 156 consecutive patients

The low-phospholipid-associated cholelithiasis syndrome (LPAC; OMIM 171060) is a peculiar form of intrahepatic cholelithiasis occurring in young adults, associated with ABCB4/MDR3 gene sequence variations. Our aim was to determine the genotype-phenotype relationships in 156 consecutive patients with the criteria of LPAC syndrome. A variant was detected in 79 (61 missense and 18 truncating sequence variants), 63 being monoallelic. The clinical features (age at onset, high prevalence in women, frequency and severity of acute and chronic complications, intrahepatic cholestasis of pregnancy [ICP]) were similar in the patients with or without ABCB4 gene sequence variation. Truncating variations were associated with an earlier onset of symptoms both in women and men. Acute and chronic biliary complications were variant-independent. Half of the women who had pregnancy developed ICP. The frequency of ICP and fetal complications were similar in patients with missense and truncating variants.

CONCLUSION

The LPAC syndrome is more frequent in women and highly associated with ICP. Half of the patients harbored missense or truncating variants of the ABCB4 gene. The characteristics of the patients without detectable variant are similar to those with variant, indicating that yet unexplored regions of the ABCB4 and other genes may be involved.

Intra-hepatic Cholestasis of Pregnancy: A Comprehensive Review

Intra-hepatic cholestasis of pregnancy is a cholestatic disorder characterized by i) pruritus, with onset in the third trimester of pregnancy, without any primary skin lesions, ii) elevated fasting serum bile acids > 10 μmol/L (and elevated serum transaminases), iii) spontaneous relief of signs and symptoms within two to three weeks after delivery, and iv) absence of other disease that cause pruritus and jaundice. It is believed to be a multi-factorial disease with interplay between genetic, environmental and hormonal factors. Incidence is between 0.02% to 2.4% of all pregnancies; with wide geographical variations. Maternal prognosis is usually good but can result in adverse fetal outcomes like meconium staining of amniotic fluid, fetal bradycardia and even fetal loss. Response to anti-histaminic is poor. Of all the medical therapies that have been described for the treatment for IHCP, ursodeoxycholic acid has the best response in relieving pruritus in mother, and probably has a role in preventing even the perinatal complications. Timely diagnosis and treatment is urged in order to prevent fetal complications and an early delivery between 37 to 38 weeks should be contemplated in severe cases, especially once fetal lung maturity is attained.

Validation of variants in SLC28A3 and UGT1A6 as genetic markers predictive of anthracycline-induced cardiotoxicity in children

BACKGROUND

The use of anthracyclines as effective antineoplastic drugs is limited by the occurrence of cardiotoxicity. Multiple genetic variants predictive of anthracycline-induced cardiotoxicity (ACT) in children were recently identified. The current study was aimed to assess replication of these findings in an independent cohort of children.

PROCEDURE

. Twenty-three variants were tested for association with ACT in an independent cohort of 218 patients. Predictive models including genetic and clinical risk factors were constructed in the original cohort and assessed in the current replication cohort.

RESULTS

. We confirmed the association of rs17863783 in UGT1A6 and ACT in the replication cohort (P = 0.0062, odds ratio (OR) 7.98). Additional evidence for association of rs7853758 (P = 0.058, OR 0.46) and rs885004 (P = 0.058, OR 0.42) in SLC28A3 was found (combined P = 1.6 × 10(-5) and P = 3.0 × 10(-5), respectively). A previously constructed prediction model did not significantly improve risk prediction in the replication cohort over clinical factors alone. However, an improved prediction model constructed using replicated genetic variants as well as clinical factors discriminated significantly better between cases and controls than clinical factors alone in both original (AUC 0.77 vs. 0.68, P = 0.0031) and replication cohort (AUC 0.77 vs. 0.69, P = 0.060).

CONCLUSIONS

. We validated genetic variants in two genes predictive of ACT in an independent cohort. A prediction model combining replicated genetic variants as well as clinical risk factors might be able to identify high- and low-risk patients who could benefit from alternative treatment options.

[Abnormal hepatic function tests in pregnancy: causes and consequences]

The well-known normal ranges of laboratory parameters are altered due to the broad spectrum of physiological changes as well as proinflammatory and procoagulant effects of pregnancy. Hepatic disorders of any aetiology can cause potential problems during gravidity. Most frequently toxic-effects, hepatotrop viruses (such as hepatitis B and C), metabolic syndrome and diseases with autoimmune background can be observed. When dealing with "pregnancy-specific hepatic syndromes", it is very important to consider the "timing-factors" of pathologic changes and deterioration of clinical pictures as well. Due to the progress in cholestasis management, early termination of pregnancy can be avoided in many cases. As the overlap is really broad between various hepatic disorders, a multidisciplinary cooperation of different sub-disciplines is emphasized in order to achieve proper diagnosis and curative measures at early phase.

Genetic determinants of cholestasis

Cholestasis is an overarching term applied for conditions whereby biliary constituents are found in the circulation because of impairment to bile flow. A variety of processes can lead to cholestasis, be they acute or chronic injuries to hepatocytes, cholangiocytes, or the broader biliary tree itself. Such injuries may be driven by rare but highly informative primary genetic abnormalities, or may be seen in individuals with a prior genetic predisposition when confronted by specific environmental challenges such as drug exposure. This review provides a broad outline of some fundamental primary genetic cholestatic syndromes and an update on varying genetic predisposition underlying several acquired cholestatic processes.

Intrahepatic cholestasis of pregnancy: new insights into its pathogenesis

AIM

To search a specific gene expression profile in women with intrahepatic cholestasis of pregnancy (ICP) and to evaluate the maternal and foetal outcome.

METHODS

We consecutively enrolled 12 women with ICP and 12 healthy pregnant controls. The gene expression profile was assayed with the microarray technique including a panel of 5541 human genes. Microarray data were validated by real-time PCR technique.

RESULTS

Caesarean delivery was performed in eight patients with ICP versus three controls (p = 0.05). ICP women delivered at earlier gestational age than control (p < 0.001). Foetal distress was recorded in two babies, but we failed to find any correlation between bile salt concentration and foetal distress. Twenty genes potentially correlated with ICP were found differentially expressed (p < 0.05). Among these, three belong to genetic classes involved in pathogenic mechanisms of ICP: (1) pathophysiology of pruritus (GABRA2, cases versus controls = 2, upregulated gene); (2) lipid metabolism and bile composition (HLPT, cases versus controls = 0.6, down-regulated gene) and (3) protein trafficking and cytoskeleton arrangement (KIFC3, cases versus controls = 0.5, down-regulated gene).

CONCLUSIONS

Different gene expression may contribute to the complex pathogenesis of ICP. An upregulation of GABRA2 receptor may indicate that GABA may play a role in the pathogenesis of pruritus in this condition.

Intrahepatic cholestasis of pregnancy levels of sulfated progesterone metabolites inhibit farnesoid X receptor resulting in a cholestatic phenotype

Intrahepatic cholestasis of pregnancy (ICP) is the most prevalent pregnancy-specific liver disease and is associated with an increased risk of adverse fetal outcomes, including preterm labor and intrauterine death. The endocrine signals that cause cholestasis are not known but 3α-sulfated progesterone metabolites have been shown to be elevated in ICP, leading us to study the impact of sulfated progesterone metabolites on farnesoid X receptor (FXR)-mediated bile acid homeostasis pathways. Here we report that the 3β-sulfated progesterone metabolite epiallopregnanolone sulfate is supraphysiologically raised in the serum of ICP patients. Mice challenged with cholic acid developed hypercholanemia and a hepatic gene expression profile indicative of FXR activation. However, coadministration of epiallopregnanolone sulfate with cholic acid exacerbated the hypercholanemia and resulted in aberrant gene expression profiles for hepatic bile acid-responsive genes consistent with cholestasis. We demonstrate that levels of epiallopregnanolone sulfate found in ICP can function as a partial agonist for FXR, resulting in the aberrant expression of bile acid homeostasis genes in hepatoma cell lines and primary human hepatocytes. Furthermore, epiallopregnanolone sulfate inhibition of FXR results in reduced FXR-mediated bile acid efflux and secreted FGF19. Using cofactor recruitment assays, we show that epiallopregnanolone sulfate competitively inhibits bile acid-mediated recruitment of cofactor motifs to the FXR-ligand binding domain.

CONCLUSION

Our results reveal a novel molecular interaction between ICP-associated levels of the 3β-sulfated progesterone metabolite epiallopregnanolone sulfate and FXR that couples the endocrine component of pregnancy in ICP to abnormal bile acid homeostasis.

Transporters in cholelithiasis

Gallstones are a common and costly disease with a projected increase in prevalence due to the increasing ageing population. Numerous endogenous and environmental factors are aetiologically related to this multifactorial disease, and genetic studies continue to unravel the pathobiological mechanisms related to gallstone formation. In particular, variants of genes encoding hepatobiliary transporters have been implicated in gallstone disease and, given their ability to influence biliary lipid composition, have undergone considerable investigation. Here we summarize the role of enterohepatic transporters in cholelithogenesis with a particular focus on pertinent ATP-binding cassette transporters (ABCB4, ABCB11, ABCC7, and ABCG5/G8).

Nuclear receptor variants in liver disease

This review aims to provide a snapshot of the actual state of knowledge on genetic variants of nuclear receptors (NR) involved in regulating important aspects of liver metabolism. It recapitulates recent evidence for the application of NR in genetic diagnosis of monogenic ("Mendelian") liver disease and their use in clinical diagnosis. Genetic analysis of multifactorial liver diseases such as viral hepatitis or fatty liver disease identifies key players in disease predisposition and progression. Evidence from these analyses points towards a role of NR polymorphisms in common diseases, linking regulatory networks to complex and variable phenotypes. The new insights into NR variants also offer perspectives and cautionary advice for their use as handles towards diagnosis and treatment.

Nuclear receptor variants in liver disease

This review aims to provide a snapshot of the actual state of knowledge on genetic variants of nuclear receptors (NR) involved in regulating important aspects of liver metabolism. It recapitulates recent evidence for the application of NR in genetic diagnosis of monogenic (“Mendelian”) liver disease and their use in clinical diagnosis. Genetic analysis of multifactorial liver diseases such as viral hepatitis or fatty liver disease identifies key players in disease predisposition and progression. Evidence from these analyses points towards a role of NR polymorphisms in common diseases, linking regulatory networks to complex and variable phenotypes. The new insights into NR variants also offer perspectives and cautionary advice for their use as handles towards diagnosis and treatment.

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.

The Multiple Facets of ABCB4 (MDR3) Deficiency

ABCB4 (MDR3), a lipid translocator, moves phosphatidylcholine from the inner to the outer leaflet of the canalicular membrane. Genetic mutations of ABCB4 lead to three distinct but related hepatobiliary diseases. Progressive familial intrahepatic cholestasis (PFIC) type 3 is a chronic cholestatic syndrome characterized by a markedly elevated gamma-glutamyltranspeptidase. Patients present with jaundice, pruritus, and hepatosplenomegaly. Periportal inflammation progresses to biliary cirrhosis and causes portal hypertension. Ursodeoxycholic acid (UDCA) normalizes liver function tests in approximately one half of treated PFIC type 3 patients. Partial responders or nonresponders eventually will require liver transplantation. Gallstone patients with ABCB4 mutations may have low phospholipid-associated cholelithiasis syndrome, characterized by cholesterol gallstones and intrahepatic microlithiasis, along with recurrent biliary symptoms, despite cholecystectomy. Patients with ABCB4 mutations also may develop intrahepatic brown pigment stones. UDCA may improve biliary symptoms even before the dissolution of stones occurs. Additional therapies such as farnesoid X receptor ligands/agonists and benzfibrates show future therapeutic promise. Intrahepatic cholestasis of pregnancy affects pregnant women with abnormal ABCB4. These women suffer from disabling pruritus and also may experience steatorrhea. Fetuses are at high risk for prematurity and stillbirths. The definitive treatment is delivery of the baby. In the interim, limited fat intake, fat-soluble vitamin supplementation, and UDCA with or without S-adenosylmethionine can provide symptomatic relief. Additional hepatobiliary diseases related to ABCB4 mutations are likely to be identified. This may result in the discovery of additional therapies for PFIC type 3, gallstones, and intrahepatic cholestasis of pregnancy.

Pruritus of unknown origin and elevated total serum bile acid levels in patients without clinically apparent liver disease

BACKGROUND AND AIM

Generalized pruritus of unknown origin (PUO) is a highly distressing condition that is unrelated to any underlying dermatologic or systemic disorder (e.g. cholestasis). Little is known about the potential contribution of elevated total serum bile acid (TSBA) levels to PUO. Our aim in the present study was to investigate the role of elevated TSBA levels in patients with PUO and the efficacy of ursodeoxycholic acid (UDCA) and cholestyramine therapy.

METHODS

Retrospective study comprising 117 patients with chronic pruritic conditions (PUO, atopic disease, asteatotic eczema, latent cholestasis, etc.); 99 patients with available TSBA levels were included and compared with healthy controls.

RESULTS

Elevated TSBA levels were detected more frequently in patients with chronic pruritic diseases than in the control population (28.28% vs 6%; P<0.001) with significantly higher pathological absolute levels (mean 17.45±34.46 µmol/L vs 6.02±4.73 µmol/L; P=0.001). Patients with PUO (n=18) showed the second-highest prevalence of pathological bile acid level elevation (83.3%; control population 6%; P<0.001), after patients with subclinical cholestasis and presented with particularly high TSBA serum values (mean 37.79±53.38 µmol/L; P<0.001). Cholestyramine (n=9) and UDCA (n=8) therapy were both effective in lowering TSBA levels and lead to substantial improvement of pruritus in patients with elevated TSBA levels.

CONCLUSIONS

Total serum bile acid levels are elevated in a high proportion of patients with PUO. These results provide evidence of a potential involvement of subclinical cholestasis in the pathogenesis of PUO. We suggest that evaluation of TSBA levels should be included in the diagnostic work-up of patients with chronic unexplained pruritus.

Liver diseases unique to pregnancy: a 2010 update

Liver disorders occurring during pregnancy may be specifically pregnancy-related, or may be due to an intercurrent or chronic liver disease, which may present in anyone, pregnant or not. This review focuses on the liver diseases unique to pregnancy. Hyperemesis gravidarum, which occurs during early pregnancy, may be associated with liver dysfunction. Intrahepatic cholestasis of pregnancy typically occurs during the second or third trimester. Pruritus and the associated biological signs of cholestasis improve rapidly after delivery. Mutations in gene encoding biliary transporters, especially ABCB4 encoding the multidrug resistance 3 protein, have been found to be associated with this complex disease. Ursodeoxycholic acid is currently the most effective medical treatment in improving pruritus and liver tests. Pre-eclampsia, which presents in late pregnancy frequently involves the liver, and HELLP syndrome (Hemolysis-Elevated Liver enzymes-Low Platelets) is a life-threatening complication. Prognosis of acute fatty liver of pregnancy has been radically transformed by early delivery, and clinicians must have a high index of suspicion for this condition when a woman presents nausea or vomiting, epigastric pain, jaundice, or polyuria-polydipsia during the third trimester. Acute fatty liver of pregnancy has been found to be associated with a defect of long-chain 3-hydroxyacyl coenzyme A dehydrogenase in the fetus, and mothers and their offspring should undergo DNA testing at least for the main associated genetic mutation (c.1528G>C).

Genetic variations of bile salt transporters as predisposing factors for drug-induced cholestasis, intrahepatic cholestasis of pregnancy and therapeutic response of viral hepatitis

INTRODUCTION

Drug-induced cholestasis, intrahepatic cholestasis of pregnancy and viral hepatitis are acquired forms of liver disease. Cholestasis is a pathophysiologic state with impaired bile formation and subsequent accumulation of bile salts in hepatocytes. The bile salt export pump (BSEP) (ABCB11) is the key export system for bile salts from hepatocytes.

AREAS COVERED

This article provides an introduction into the physiology of bile formation followed by a summary of the current knowledge on the key bile salt transporters, namely, the sodium-taurocholate co-transporting polypeptide NTCP, the organic anion transporting polypeptides (OATPs), BSEP and the multi-drug resistance protein 3. The pathophysiologic consequences of altered functions of these transporters, with an emphasis on molecular and genetic aspects, are then discussed.

EXPERT OPINION

Knowledge of the role of hepatocellullar transporters, especially BSEP, in acquired cholestasis is continuously increasing. A common variant of BSEP (p.V444A) is now a well-established susceptibility factor for acquired cholestasis and recent evidence suggests that the same variant also influences the therapeutic response and disease progression of viral hepatitis C. Studies in large independent cohorts are now needed to confirm the relevance of p.V444A. Genome-wide association studies should lead to the identification of additional genetic factors underlying cholestatic liver disease.

Inflammatory pseudo-tumor of the liver: a rare pathological entity

Inflammatory pseudo-tumor (IPT) of the liver is a rare benign neoplasm and is often mistaken as a malignant entity. Few cases have been reported in the literature and the precise etiology of inflammatory pseudotumor remains unknown. Patients usually present with fever, abdominal pain and jaundice. The proliferation of spindled myofibroblast cells mixed with variable amounts of reactive inflammatory cells is characteristics of IPT. We reviewed the literature regarding possible etiology for IPT with a possible suggested etiology.

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

OBJECTIVES

The aim of the study was to estimate the frequency of ABCB4 mutations among children with chronic intrahepatic cholestasis with elevated gamma-glutamyl-transpeptidase (γ-GT) activity and to characterize the genotypes with respect to severity of symptoms, response to ursodeoxycholic acid therapy, and outcome.

PATIENTS AND METHODS

Molecular analysis of ABCB4 in 133 Italian children was performed, and ABCB4 mutations were classified as disease-causing mutations or benign substitutions according to the prediction algorithm PolyPhen.

RESULTS

: Twenty-eight patients were identified carrying 31 mutations (20 disease causing). Twenty patients carried 2 mutated alleles and 8 only 1. At presentation (1-204 months), 20 children were symptomatic with jaundice and/or pruritus, whereas in 8 biochemical cholestasis was a fortuitous finding. Cirrhosis developed in 15 and 6 progressed to terminal liver failure. Disease-causing mutations on both alleles were found to be associated with reduced liver expression of ABCB4 protein, lack of response to ursodeoxycholic acid therapy, and progression to cirrhosis and end-stage liver disease, whereas mild genotypes, including single heterozygous mutations, were generally associated with less severe disease and, often, absence of symptoms.

CONCLUSIONS

ABCB4 mutations are responsible for a chronic liver disease in more than one-third of patients with chronic intrahepatic cholestasis and elevated γ-GT activity. In patients with severe ABCB4 genotype, the disease is often progressive with risk of developing cirrhosis and liver failure during the first 2 decades of life. Patients with mild genotypes, including single heterozygous mutations, have variable expressions of liver disease that may be influenced by comorbidity factors and modulated by still unknown genetic modifiers.

Analysis of gene mutations in children with cholestasis of undefined etiology

BACKGROUND

The discovery of genetic mutations in children with inherited syndromes of intrahepatic cholestasis allows for diagnostic specificity despite similar clinical phenotypes. Here, we aimed to determine whether mutation screening of target genes could assign a molecular diagnosis in children with idiopathic cholestasis.

PATIENTS AND METHODS

DNA samples were obtained from 51 subjects with cholestasis of undefined etiology and surveyed for mutations in the genes SERPINA1, JAG1, ATP8B1, ABCB11, and ABCB4 by a high-throughput gene chip. Then, the sequence readouts for all 5 genes were analyzed for mutations and correlated with clinical phenotypes. Healthy subjects served as controls.

RESULTS

Sequence analysis of the genes identified 14 (or 27%) subjects with missense, nonsense, deletion, and splice site variants associated with disease phenotypes based on the type of mutation and/or biallelic involvement in the JAG1, ATP8B1, ABCB11, or ABCB4 genes. These patients had no syndromic features and could not be differentiated by biochemical markers or histopathology. Among the remaining subjects, 10 (or ∼20%) had sequence variants in ATP8B1 or ABCB11 that involved only 1 allele, 8 had variants not likely to be associated with disease phenotypes, and 19 had no variants that changed amino acid composition.

CONCLUSIONS

Gene sequence analysis assigned a molecular diagnosis in 27% of subjects with idiopathic cholestasis based on the presence of variants likely to cause disease phenotypes.

Familial cholestasis: progressive familial intrahepatic cholestasis, benign recurrent intrahepatic cholestasis and intrahepatic cholestasis of pregnancy

Progressive familial intrahepatic cholestasis (PFIC) type 1, 2 and 3 are due to mutations in ATP8B1, ABCB11 and ABCB4, respectively. Each of these genes encodes a hepatocanalicular transporter, which is essential for the proper formation of bile. Mutations in ABCB4 can result in progressive cholestatic disease, while mutations in ATP8B1 and ABCB11 can result both in episodic cholestasis, referred to as benign recurrent intrahepatic cholestasis (BRIC) type 1 and 2, as well as in progressive cholestatic disease. This suggests a clinical continuum and these diseases are therefore preferably referred to as ATP8B1 deficiency and ABCB11 deficiency. Similarly PFIC type 3 is designated as ABCB4 deficiency. Heterozygous mutations in each of these transporters can also be associated with intrahepatic cholestasis of pregnancy. This review summarizes the pathophysiology, clinical features and current as well as future therapeutic options for progressive familial- and benign recurrent intrahepatic cholestasis as well as intrahepatic cholestasis of pregnancy.

Liver disease associated with canalicular transport defects: current and future therapies

Bile formation at the canalicular membrane is a delicate process. This is illustrated by inherited liver diseases due to mutations in ATP8B1, ABCB11, ABCB4, ABCC2 and ABCG5/8, all encoding hepatocanalicular transporters. Effective treatment of these canalicular transport defects is a clinical and scientific challenge that is still ongoing. Current evidence indicates that ursodeoxycholic acid (UDCA) can be effective in selected patients with PFIC3 (ABCB4 deficiency), while rifampicin reduces pruritus in patients with PFIC1 (ATP8B1 deficiency) and PFIC2 (ABCB11 deficiency), and might abort cholestatic episodes in BRIC (mild ATP8B1 or ABCB11 deficiency). Cholestyramine is essential in the treatment of sitosterolemia (ABCG5/8 deficiency). Most patients with PFIC1 and PFIC2 will benefit from partial biliary drainage. Nevertheless liver transplantation is needed in a substantial proportion of these patients, as it is in PFIC3 patients. New developments in the treatment of canalicular transport defects by using nuclear receptors as a target, enhancing the expression of the mutated transporter protein by employing chaperones, or by mutation specific therapy show substantial promise. This review will focus on the therapy that is currently available as well as on those developments that are likely to influence clinical practice in the near future.

Drug-induced liver injury: insights from genetic studies

Drug-induced liver injury (DILI) is an increasing health problem and a challenge for physicians, regulatory bodies and the pharmaceutical industry, not only because of its potential severity and elusive pathogenesis but also because it is often inaccurately diagnosed, commonly missed entirely and more often not reported. The general view is that idiosyncratic DILI, which is not predictable whether based on the pharmacology of the drug or on the dose administered, is determined by the presence in the recipient of variants in, or expression of, genes coding for key metabolic pathways and/or the immune response, and the interaction of these genetic variants with environmental variables. Furthermore, idiosyncratic DILI is an example of a complex-trait disease with two or more susceptibility loci, as reflected by the frequency of genetic variants in the population often being higher than the occurrence of significant liver injury. Polymorphisms of bioactivation/toxification pathways via the CYP450 enzymes (Phase I), detoxification reactions (Phase II) and excretion/transport (Phase III), together with immunological factors that might determine DILI are reviewed. Challenges such as gene-trait association studies and whole-genome studies, and future approaches to the study of DILI are explored. Better knowledge of the candidate genes involved could provide further insight for the prospective identification of susceptible patients at risk of developing drug-induced hepatotoxicity, development of new diagnostic tools and new treatment strategies with safer drugs.

Impact of experimental colitis on hepatobiliary transporter expression and bile duct injury in mice

BACKGROUND AND AIMS

The pathogenetic link between ulcerative colitis and sclerosing cholangitis (SC) is unclear. We hypothesized that colitis induces changes in bile composition via inflammation-induced reduction of hepatobiliary transporter gene expression, ultimately resulting in cholestasis and bile duct injury.

METHODS

Alterations in transporter expression and bile secretion in acute dextran sulphate sodium (DSS)-induced colitis were compared with lipopolysaccharide (LPS)-treated mice serving as positive control. Whether chronic DSS-colitis elicits cholangitis in genetically predisposed animals was studied in heterozygous multidrug resistance gene 2 knockout mice (Mdr2(+/-)).

RESULTS

LPS but not DSS-colitis changed major hepatobiliary transporters (Ntcp, Bsep, Mrp2-4, Ostalpha/beta, Abcg5/8, Oatp1-4, Mdr1b and Mdr2), enzymes (Cyp3a11 and Cyp7a1), nuclear receptors (RXRalpha, FXR, CAR and PXR) and proinflammatory mediators (tumour necrosis factor alpha and inducible nitric oxide synthase). Formation of toxic bile reflected by an increased bile acid/phospholipid ratio was observed neither in acute nor in chronic colitis, although heterozygous Mdr2(+/-) mice developed mild portal inflammation after chronic colitis.

CONCLUSIONS

In contrast to LPS, DSS-colitis has a minor impact on hepatobiliary gene expression and bile secretion. Therefore, intestinal inflammation-associated changes of hepatobiliary transporter expression do not play a pathogenetic role in SC.

[Right upper quadrant abdominal pain and fever. Genetic phospholipid deficiency]

A 35-year-old woman is referred for right upper quadrant abdominal pain and fever. She had a cholecystectomy for gallstones 4 years previously. An aunt has also had a cholecystectomy. Abdominal ultrasound examination shows numerous hyperechoic foci within the liver and some "comet tail" artifacts. Because of her age (less than 40), the recurrence of biliary symptoms after cholecystectomy, her family history and the intrahepatic hyperechoic foci, the diagnosis of low phospholipid-associated cholelithiasis (LPAC) syndrome is suspected and confirmed by the demonstration of a point mutation of the ABCB4 gene. Therapy by ursodeoxycholic acid (AUDC) is started. Symptoms improve and they disappear completely within a few weeks. The cause, pathophysiology, diagnosis and treatment are reviewed.

Allograft steatohepatitis in progressive familial intrahepatic cholestasis type 1 after living donor liver transplantation

We studied histological features and long-term outcomes in patients with progressive familial intrahepatic cholestasis type 1 (PFIC1) after liver transplantation (LT). Histological findings were correlated with the post-LT course and treatment in 11 recipients with PFIC1. Ages at LT varied from 1 to 18 years (median, 4 years). Macrovesicular steatosis was observed in 8 patients at a median of 60 days post-LT (range, 21-191 days). Severe steatosis progressed to steatohepatitis in 7 patients at a median of 161 days (range, 116-932 days). The patients were followed up for a median of 7.3 years (range, 2.3-16.1 years). Six showed bridging fibrosis, with 2 progressing to cirrhosis. One patient with cirrhosis died because of the rupture of a splenic artery aneurysm 13.6 years post-LT. Post-LT refractory diarrhea was present in all 8 having steatosis. Three without post-LT diarrhea showed no allograft steatosis. Bile adsorptive resin therapy reduced the diarrhea and steatosis. Patients with posttransplant steatosis typically had more severe mutations of the ATPase class I type 8B member 1 (ATP8B1) gene and were more likely to have systemic complications such as pancreatitis. In conclusion, allograft steatosis was present in patients with PFIC1, progressing to steatohepatitis and cirrhosis. Because expression of the familial intrahepatic cholestasis 1 gene occurs in several organs, including the small intestine, pancreas, and liver, and it is involved in enterohepatic bile acid circulation, post-LT steatosis may be due to a malfunction of the ATP8B1 product.

Intrahepatic cholestasis of pregnancy

Intrahepatic cholestasis of pregnancy (ICP) is a pregnancy-specific liver disorder characterized by maternal pruritus in the third trimester, raised serum bile acids and increased rates of adverse fetal outcomes. The etiology of ICP is complex and not fully understood, but it is likely to result from the cholestatic effects of reproductive hormones and their metabolites in genetically susceptible women. Equally unclear are the mechanisms by which the fetal complications occur. This article reviews the epidemiology, clinical features, diagnosis, etiology and management of ICP.

A missense mutation in ABCB4 gene involved in progressive familial intrahepatic cholestasis type 3 leads to a folding defect that can be rescued by low temperature

Progressive familial intrahepatic cholestasis type 3 (PFIC3) is a rare liver disease characterized by early onset of cholestasis that leads to cirrhosis and liver failure before adulthood. PFIC3 may be improved by chronic administration of ursodeoxycholic acid, although in many cases liver transplantation is the only therapy. The disease is caused by mutations of the adenosine triphosphate (ATP)-binding cassette, sub-family B, member 4 (ABCB4) [multidrug resistance 3 (MDR3)] gene encoding a specific hepatocellular canalicular transporter involved in biliary phosphatidylcholine secretion. Several mutations have been reported; however, the effect of individual mutations has not been investigated. ABCB4 is highly homologous to ATP-binding cassette, sub-family B, member 1 (ABCB1) (MDR1), the multidrug transporter responsible for drug resistance of cancer cells. We have studied the effect of mutation I541F localized to the first nucleotide-binding domain, which is highly conserved between ABCB4 and ABCB1. Plasmids encoding the wild-type human ABCB4 or rat ABCB1-green fluorescing protein (GFP) construct, and corresponding I541F-mutants, were expressed in hepatocellular carcinoma, human (HepG2) and Madin-Darby canine kidney (MDCK) cells. Expression studies showed that ABCB4 was localized at the bile canalicular membrane in HepG2 cells and at the apical surface in MDCK cells, whereas the I541F mutant was intracellular. In MDCK cells, ABCB1-I541F also accumulated intracellularly in compartments, which were identified as the endoplasmic reticulum and cis-Golgi, and remained partially endoH-sensitive. After shifting cells to 27 degrees C, ABCB1-I541F was expressed at the apical cell surface in a mature and active form. Similarly, ABCB4 was significantly trafficked to the membrane of bile canaliculi in HepG2 cells.

CONCLUSION

Mutation I541F causes mislocalization of both ABCB4 and ABCB1. Intracellular retention of ABCB4-I541F can explain the disease in PFIC3 patients bearing this mutation. The observation that plasma membrane expression and activity can be rescued by low temperature opens perspectives to develop novel therapies for the treatment of PFIC3.

Liver disease in pregnancy

Liver diseases in pregnancy may be categorized into liver disorders that occur only in the setting of pregnancy and liver diseases that occur coincidentally with pregnancy. Hyperemesis gravidarum, preeclampsia/eclampsia, syndrome of hemolysis, elevated liver tests and low platelets (HELLP), acute fatty liver of pregnancy, and intrahepatic cholestasis of pregnancy are pregnancy-specific disorders that may cause elevations in liver tests and hepatic dysfunction. Chronic liver diseases, including cholestatic liver disease, autoimmune hepatitis, Wilson disease, and viral hepatitis may also be seen in pregnancy. Management of liver disease in pregnancy requires collaboration between obstetricians and gastroenterologists/hepatologists. Treatment of pregnancy-specific liver disorders usually involves delivery of the fetus and supportive care, whereas management of chronic liver disease in pregnancy is directed toward optimizing control of the liver disorder. Cirrhosis in the setting of pregnancy is less commonly observed but offers unique challenges for patients and practitioners. This article reviews the epidemiology, pathophysiology, diagnosis, and management of liver diseases seen in pregnancy.

The role of the photoreceptor ABC transporter ABCA4 in lipid transport and Stargardt macular degeneration

ABCA4 is a member of the ABCA subfamily of ATP binding cassette (ABC) transporters that is expressed in rod and cone photoreceptors of the vertebrate retina. ABCA4, also known as the Rim protein and ABCR, is a large 2,273 amino acid glycoprotein organized as two tandem halves, each containing a single membrane spanning segment followed sequentially by a large exocytoplasmic domain, a multispanning membrane domain and a nucleotide binding domain. Over 500 mutations in the gene encoding ABCA4 are associated with a spectrum of related autosomal recessive retinal degenerative diseases including Stargardt macular degeneration, cone-rod dystrophy and a subset of retinitis pigmentosa. Biochemical studies on the purified ABCA4 together with analysis of abca4 knockout mice and patients with Stargardt disease have implicated ABCA4 as a retinylidene-phosphatidylethanolamine transporter that facilitates the removal of potentially reactive retinal derivatives from photoreceptors following photoexcitation. Knowledge of the genetic and molecular basis for ABCA4 related retinal degenerative diseases is being used to develop rationale therapeutic treatments for this set of disorders.

Progressive familial intrahepatic cholestasis

Progressive familial intrahepatic cholestasis (PFIC) refers to heterogeneous group of autosomal recessive disorders of childhood that disrupt bile formation and present with cholestasis of hepatocellular origin. The exact prevalence remains unknown, but the estimated incidence varies between 1/50,000 and 1/100,000 births.

Three types of PFIC have been identified and related to mutations in hepatocellular transport system genes involved in bile formation. PFIC1 and PFIC2 usually appear in the first months of life, whereas onset of PFIC3 may also occur later in infancy, in childhood or even during young adulthood. Main clinical manifestations include cholestasis, pruritus and jaundice. PFIC patients usually develop fibrosis and end-stage liver disease before adulthood. Serum gamma-glutamyltransferase (GGT) activity is normal in PFIC1 and PFIC2 patients, but is elevated in PFIC3 patients. Both PFIC1 and PFIC2 are caused by impaired bile salt secretion due respectively to defects in ATP8B1 encoding the FIC1 protein, and in ABCB11 encoding the bile salt export pump protein (BSEP). Defects in ABCB4, encoding the multi-drug resistant 3 protein (MDR3), impair biliary phospholipid secretion resulting in PFIC3.

Diagnosis is based on clinical manifestations, liver ultrasonography, cholangiography and liver histology, as well as on specific tests for excluding other causes of childhood cholestasis. MDR3 and BSEP liver immunostaining, and analysis of biliary lipid composition should help to select PFIC candidates in whom genotyping could be proposed to confirm the diagnosis. Antenatal diagnosis can be proposed for affected families in which a mutation has been identified. Ursodeoxycholic acid (UDCA) therapy should be initiated in all patients to prevent liver damage. In some PFIC1 or PFIC2 patients, biliary diversion can also relieve pruritus and slow disease progression. However, most PFIC patients are ultimately candidates for liver transplantation. Monitoring of hepatocellular carcinoma, especially in PFIC2 patients, should be offered from the first year of life. Hepatocyte transplantation, gene therapy or specific targeted pharmacotherapy may represent alternative treatments in the future.

Sequencing and functional assessment of hPXR (NR1I2) variants in intrahepatic cholestasis of pregnancy

1. The purpose of this study was to evaluate the role of coding variation in hPXR (NR1I2) in intrahepatic cholestasis of pregnancy (ICP) and to functionally asses the response of PXR variants to ligands of interest in ICP. 2. The coding region of hPXR was sequenced in a cohort of 121 Caucasian ICP patients and exon 2 was sequenced in an additional 226 cases. Reporter assays were used to evaluate the function of all known hPXR variants in response to the secondary bile acid lithocholic acid and therapeutic agents rifampicin, ursodeoxycholic acid and dexamethasone. 3. Two coding single nucleotide polymorphisms (C79T and G106A) were detected in the ICP cohort at frequencies consistent with healthy populations. These do not alter hPXR function in response to ligands of interest to ICP. Analysis of all known coding hPXR variants demonstrates that while subtle changes in experimental design mask or may unveil the functional effects of genetic variation, these are not maintained in a standard functional assay. 4. Coding genetic variation in hPXR does not contribute to the aetiology of ICP in Caucasian populations.

The molecular genetics of intrahepatic cholestasis of pregnancy

Intrahepatic cholestasis of pregnancy (ICP), also known as obstetric cholestasis, causes maternal pruritus and liver impairment, and may be complicated by spontaneous preterm labour, fetal asphyxial events and intrauterine death. Our understanding of the aetiology of this disease has expanded significantly in the last decade due to a better understanding of the role played by genetic factors. In particular, advances in our knowledge of bile homeostasis has led to the identification of genes that play a considerable role in susceptibility to ICP. In this review we consider these advances and discuss the disease in the context of bile synthesis and metabolism, focusing on the genetic discoveries that have shed light on the molecular aetiology and pathophysiology of the condition.

Intrahepatic cholestasis of pregnancy-current achievements and unsolved problems

Intrahepatic cholestasis of pregnancy (ICP) is the most common pregnancy-related liver disorder. Maternal effects of ICP are mild; however, there is a clear association between ICP and higher frequency of fetal distress, preterm delivery, and sudden intrauterine fetal death. The cause of ICP remains elusive, but there is evidence that mutations in genes encoding hepatobiliary transport proteins can predispose for the development of ICP. Recent data suggest that ursodeoxycholic acid is currently the most effective pharmacologic treatment, whereas obstetric management is still debated. Clinical trials are required to identify the most suitable monitoring modalities that can specifically predict poor perinatal outcome. This article aims to review current achievements and unsolved problems of ICP.

A mutation in the canalicular phospholipid transporter gene, ABCB4, is associated with cholestasis, ductopenia, and cirrhosis in adults

Cholestatic liver disease (CLD) is a major cause of progressive liver damage and liver failure. Several forms of biliary cirrhosis are caused by mutations in specific genes. We sought to identify a genetic defect in a family with CLD impossible to assign to a distinct pathogenic entity. Clinical and histopathological characterization of the family members, microarray-based single-nucleotide polymorphism genotyping, and analysis of candidate genes were performed. Among six of 11 siblings severely affected by idiopathic CLD in a family from a population isolate in Transylvania, three died of cirrhosis (aged 5, 7, and 43 years) and three had adult-onset disease with small duct cholangiopathy, including ductopenia. Others were mildly affected and experienced intrahepatic cholestasis of pregnancy, miscarriages, or stillbirth. Pedigree studies revealed distant parental consanguinity. Genome-wide linkage analysis and autozygosity mapping yielded a single maximal lod-score of 3.88 on chromosome 7q21.1-7q22, excluding other genomic loci. Sequencing of ABCB4 at this locus revealed a novel missense mutation c.2362C>T (p.Arg788Trp) which cosegregated with severity of disease. Bile from a mutation homozygote showed a reduced phosphatidylcholine/bile acid ratio, consistent with reduced ABCB4 phosphatidylcholine transport activity.

CONCLUSION

We show that a missense mutation in ABCB4 is a cause for ductopenic CLD in adulthood. Allelic status correlated with severity of liver disease ranging from intrahepatic cholestasis of pregnancy through fibrosis to cirrhosis and death in childhood and adulthood. Mutational analysis of ABCB4 should be generally considered in all patients with cholestatic liver disease of unknown etiology regardless of age and onset of disease.