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

Association between ABCB4 variants and intrahepatic cholestasis of pregnancy

The ABCB4 gene encodes multidrug resistance protein 3(MDR3), which is a phosphatidylcholine(PC) transfer enzyme that transfers lecithin from the inner part of the phospholipid bilayer to the extracellular bile. The occurrence of intrahepatic cholestasis of pregnancy(ICP) is closely related to ABCB4 variants, but there is limited research on this topic in southern Anhui, China. We sequenced ABCB4 in pregnant women with ICP and healthy pregnant women to explore the relationship. A total of 30 patients diagnosed with ICP were selected as the study objects and 90 healthy pregnant women were selected as the control group. DNA was extracted from peripheral blood of ICP patients and healthy pregnant women, 27 exons were sequencing by Sanger sequencing. Polymerase chain reaction (PCR) was used to amplify those exons. PolyPhen2, Mutation Taster, Provean, SIFT and Mutpred2 were used to predict protein structure, and Pymol software was used to predict the impact of missense variant c.1954 A > G(p.Arg652Gly) on proteins. Four exonic variants of ABCB4 gene were detected in ICP patients and healthy pregnant women, including synonymous variants c.175 C > T, c.504 C > T,c.711 A > T and missense variant c.1954 A > G(p.Arg652Gly). The incidence of the missense variant c.1954 A > G(p.Arg652Gly) was 6/90 in healthy pregnant womenand 8/30 in ICP patients.In healthy pregnant women with the missense variant c.1954 A > G(p.Arg652Gly), no other exonic variants were found. In ICP patients with missense variant c.1954 A > G(p.Arg652Gly), other exonic variants were found. PolyPhen2, Mutation Taster, Provean, SIFT and Mutpred2 were used to predict that the four exonic variants were benign, while Pymol was used to showed that the missense variant was located in the linker region of MDR3 and had a slight impact on protein function. Among ICP patients with missense variant c.1954 A > G(p.Arg652Gly), patients with three exonic variants(c.504 C > T, c.711 A > T, c.1954 A > G) had higher γ-GT, TBA, ALT and AST than those with two exonic variants. ABCB4 missense variant c.1954 A > G(p.Arg652Gly) requires the combination of other variants(c.175 C > T, c.504 C > T,c.711 A > T) to cause ICP symptoms, and when combined with other variants, it has a superimposed effect.

A novel heterozygous deletion in ABCB4 gene in a Chinese family with intrahepatic cholestasis of pregnancy, neonatal hyperbilirubinemia, and cholelithiasis: Case reports and literature review

BACKGROUND

ABCB4 gene (OMIM *171060) variant is associated with a wide clinical spectrum of hepatobiliary diseases, including familial intrahepatic cholestasis of pregnancy (ICP), progressive familial intrahepatic cholestasis type 3 (PFIC3), and neonatal hyperbilirubinemia due to impaired protection of the bile duct. The majority of reported cases, however, were missense or nonsense variants, with few deletion variant findings in the Chinese population.

METHOD

We performed whole genome sequencing and confirmed it with Sanger sequencing of the proband infant and his families. Clinical courses and laboratory results were documented and collected from the proband infant and his mother. We also reviewed other published cases related to genetic variants in ABCB4 in the Chinese population.

RESULTS

A 26-year-old Chinese female (II.2) who had recurrent intrahepatic cholestasis of pregnancy and her 49-day-old son (III.4) who had hyperbilirubinemia, both presented with extremely elevated total bile acid, cholestatic dominant pattern liver function abnormalities. They were able to stay relatively stable with mild pruritus on ursodeoxycholic acid treatment. After ruling out other possibilities, genetic sequencing revealed a diagnosis of heterozygous deletion variant NM_018849.3:c.1452_1454del (NP_061337.1:p.Thr485del) in ABCB4, which was not reported before, in the symptomatic mother (II.2), index patient (III.4), and the symptomatic grandmother (I.2). This variant resulted in clinical spectrums of ICP, neonatal hyperbilirubinemia, and cholelithiasis in our pedigree.

CONCLUSION

We reported a novel heterozygous deletion variant of the ABCB4 gene in a Chinese family, as well as a literature review of ABCB4-related disorders. We aim to facilitate healthcare professionals to better understand genetic factors as an uncommon cause of hepatobiliary diseases, as well as improve therapeutic strategies in challenging clinical situations such as pregnancy and neonatal care.

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.

Clinical characteristics and prognosis of primary hepatolithiasis in hospitalized children

The purpose of this study is to evaluate the clinical characteristics and prognosis of primary hepatolithiasis in hospitalized children. This retrospective cohort study included 106 hospitalized patients with primary hepatolithiasis at Beijing Children's Hospital. Clinical data were derived from electronic inpatient (2010-2021) and outpatient (2016-2021) medical records. The prognosis was evaluated by outpatient ultrasounds after discharge and telephone interviews performed in December 2022. Intrahepatic bile duct stones in patients enrolled in the study were all found incidentally by abdominal ultrasound during hospitalization, with an incidence of 1.7 per 10,000 hospitalized children. The mean age at diagnosis was 9.3 ± 3.6 years, with male predominance (69/106, 65.1%). The right lobe of the liver (80/106, 75.5%) was preferentially affected. All patients underwent conservative observation. Seventy-eight patients (78/106, 73.6%) were followed up with a mean follow-up age of 17.1 ± 5.0 years, and 4 (4/78, 5.1%) had intermittent abdominal pain. From 2016 to 2021, 32 patients were diagnosed with primary hepatolithiasis, and follow-up abdominal ultrasounds were performed in 20 of them (20/32, 60.0%) with a median time of 2.1 (0.1, 3.5) years. The stones were present in 17 patients (17/20, 85.0%).

CONCLUSION

Primary hepatolithiasis in hospitalized children is rare, almost found accidentally; mostly affects the right lobe of the liver; and can be conservatively observed without surgical treatment in childhood.

WHAT IS KNOWN

• Primary hepatolithiasis in adults often presents with severe clinical symptoms and requires hepatectomy.. • There are few studies on primary hepatolithiasis in children.

WHAT IS NEW

• Primary hepatolithiasis in children is mostly found accidentally by abdominal ultrasound without associated symptoms during hospitalization. • Children with accidental primary hepatolithiasis can be conservatively observed without surgical treatment in childhood.

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 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.

Biallelic loss-of-function ZFYVE19 mutations are associated with congenital hepatic fibrosis, sclerosing cholangiopathy and high-GGT cholestasis

BACKGROUND

For many children with intrahepatic cholestasis and high-serum gamma-glutamyl transferase (GGT) activity, a genetic aetiology of hepatobiliary disease remains undefined. We sought to identify novel genes mutated in children with idiopathic high-GGT intrahepatic cholestasis, with clinical, histopathological and functional correlations.

METHODS

We assembled a cohort of 25 children with undiagnosed high-GGT cholestasis and without clinical features of biliary-tract infection or radiological features of choledochal malformation, sclerosing cholangitis or cholelithiasis. Mutations were identified through whole-exome sequencing and targeted Sanger sequencing. We reviewed histopathological findings and assessed phenotypical effects of ZFYVE19 deficiency in cultured cells by immunofluorescence microscopy.

RESULTS

Nine Han Chinese children harboured biallelic, predictedly complete loss-of-function pathogenic mutations in ZFYVE19 (c.314C>G, p.S105X; c.379C>T, p.Q127X; c.514C>T, p.R172X; c.547C>T, p.R183X; c.226A>G, p.M76V). All had portal hypertension and, at liver biopsy, histopathological features of the ductal plate malformation (DPM)/congenital hepatic fibrosis (CHF). Four children required liver transplantation for recurrent gastrointestinal haemorrhage. DPM/CHF was confirmed at hepatectomy, with sclerosing small-duct cholangitis. Immunostaining for two primary-cilium axonemal proteins found expression that was deficient intraluminally and ectopic within cholangiocyte cytoplasm. ZFYVE19 depletion in cultured cells yielded abnormalities of centriole and axoneme.

CONCLUSION

Biallelic ZFYVE19 mutations can lead to high-GGT cholestasis and DPM/CHF in vivo. In vitro, they can lead to centriolar and axonemal abnormalities. These observations indicate that mutation in ZFYVE19 results, through as yet undefined mechanisms, in a ciliopathy.

Novel ABCB4 mutation in a Chinese female patient with progressive familial intrahepatic cholestasis type 3: a case report

Background

Progressive familial intrahepatic cholestasis (PFIC) is a rare group of autosomal recessive hereditary hepatic diseases. There are three types of PFIC, classified according to the mutated gene. For example, PFIC type 3 (PFIC3) is due to mutations in the ABCB4 gene (encoding multidrug-resistant protein 3 [MDR3]).

Case presentation

We present a 19-year-old Chinese female patient who had a 2-year history of recurrent liver dysfunction, with mainly elevated alkaline phosphatase and γ-glutamyl transpeptidase(γ-GT) levels. After excluding other causes of abnormal liver function and cholestasis, the final diagnosis of PFIC3 was confirmed by histopathological examination and gene detection. The immunohistochemical results showed no MDR3 protein expression in the bile duct membrane. Genetic sequencing analysis revealed a novel heterozygous 2137G > A; p. V713M mutation (Exon 17) and a synonymous 504C > T; p. N168N mutation (Exon 6) in ABCB4.

Conclusions

Our patient with long-term liver dysfunction demonstrated that elevated alkaline phosphatase and γ-GT levels should be associated with the diagnosis of PFIC3, and gene detection is the key to diagnosis. From our in silico analysis, the novel mutation p. V713M in Exon 17 was predicted to affect protein function, with a SIFT (Sorting Intolerant from Tolerant) score of 0.02, indicating a deleterious effect. Further studies are necessary to investigate the impact of the novel heterozygous 2137G > A; p. V713M mutation (Exon 17) on functional defects of MDR3 and PFIC3.

Molecular findings in children with inherited intrahepatic cholestasis

BACKGROUND

Genetic defects account for a substantial proportion of pediatric cholestasis. This study explored the molecular findings in a large cohort of Chinese patients with inherited cholestasis.

METHODS

Between January 2012 and June 2016, 809 Chinese pediatric patients with suspected inherited intrahepatic cholestasis were evaluated by Sanger sequencing and/or panel sequencing.

RESULTS

Of the 809 patients, 273 (33.7%) obtained a genetic diagnosis. The rate of positive genetic diagnosis in patients with disease onset at 0-3 month of age was higher than that in patients with disease onset at 4 month of age or later. There were 17 distinct genetic defects diagnosed. The top 4 resulted from mutations in SLC25A13 (44.3%), JAG1 (24.5%), ABCB11 (11.0%), and ATP8B1 (5.9%). All 17 genetic disorders were diagnosed in patients with disease onset at 0-3 months of age; but only 5 were diagnosed in patients with disease onset beyond 4 months of age. A total of 217 distinct pathogenic variants, including 41 novel variants, were identified. Ten recurrent mutations were detected in SLC25A13, ATP8B1, and CYP27A1. They accounted for 48.2% of the total 477 mutant alleles.

CONCLUSIONS

There were 17 distinct genetic disorders diagnosed in Chinese pediatric patients with inherited cholestasis.

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).

A Specially Designed Multi-Gene Panel Facilitates Genetic Diagnosis in Children with Intrahepatic Cholestasis: Simultaneous Test of Known Large Insertions/Deletions

BACKGROUND AND AIMS

Large indels are commonly identified in patients but are not detectable by routine Sanger sequencing and panel sequencing. We specially designed a multi-gene panel that could simultaneously test known large indels in addition to ordinary variants, and reported the diagnostic yield in patients with intrahepatic cholestasis.

METHODS

The panel contains 61 genes associated with cholestasis and 25 known recurrent large indels. The amplicon library was sequenced on Ion PGM system. Sequencing data were analyzed using a routine data analysis protocol and an internal program encoded for large indels test simultaneously. The validation phase was performed using 54 patients with known genetic diagnosis, including 5 with large insertions. At implement phase, 141 patients with intrahepatic cholestasis were evaluated.

RESULTS

At validation phase, 99.6% of the variations identified by Sanger sequencing could be detected by panel sequencing. Following the routine protocol, 99.8% of false positives could be filtered and 98.8% of retained variations were true positives. Large insertions in the 5 patients with known genetic diagnosis could be correctly detected using the internal program. At implementation phase, 96.9% of the retained variations, following the routine protocol, were confirmed to be true. Twenty-nine patients received a potential genetic diagnosis when panel sequencing data were analyzed using the routine protocol. Two additional patients, who were found to harbor large insertions in SLC25A13, obtained a potential genetic diagnosis when sequencing data were further analyzed using the internal program. A total of 31 (22.0%) patients obtained a potential genetic diagnosis. Nine different genetic disorders were diagnosed, and citrin deficiency was the commonest.

CONCLUSION

Specially designed multi-gene panel can correctly detect large indels simultaneously. By using it, we assigned a potential genetic diagnosis to 22.0% of patients with intrahepatic cholestasis.

The Features of GGT in Patients with ATP8B1 or ABCB11 Deficiency Improve the Diagnostic Efficiency

Background and Aims

Genetic defects in ATP8B1 or ABCB11 account for the majority of cholestasis with low GGT. But the ranges for GGT in patients with ATP8B1 or ABCB11 deficiency are unclear. This study tried to unravel the features of GGT in these patients that improve diagnostic efficiency.

Methods

This study enrolled 207 patients with chronic cholestasis who were ordered to test for ATP8B1 and/or ABCB11 from January 2012 to December 2015. Additional 17 patients with ATPB81 or ABCB11 deficiency diagnosed between January 2004 and December 2011 were also enrolled in this study. 600 population-matched children served as controls. Clinical data were obtained by retrospectively reviewing medical records.

Results

A total of 26 patients were diagnosed with ATP8B1 deficiency and 30 patients were diagnosed with ABCB11 deficiency. GGT levels were similar between the two disorders at any observed month of age, but varied with age. The peak GGT value was <70U/L in the 2nd~6th month of life, <60U/L in the 7th~12th month and <50U/L beyond one year. GGT levels in patients with a genetic diagnosis were different from that in patients without a genetic diagnosis and controls. Larger ranges for GGT were found in patients without a genetic diagnosis. Some controls had GGT≥70U/L in the 2nd~6th month. Of the 207 patients, 39 (18.8%) obtained a genetic diagnosis. 111 patients met the ranges described above, including all the 39 patients with ATP8B1 or ABCB11 deficiency. The sensitivity was 100.0%. The rate of a positive molecular diagnosis increased to 35.1% (39/111 vs. 39/207, X² = 10.363, P = 0.001). The remaining 96 patients exceeded the ranges described above and failed to receive a genetic diagnosis. These patients accounted for 43.8% of sequencing cost.

Conclusions

GGT levels in patients with ATP8B1 or ABCB11 deficiency varied with age. The peak GGT value was <70U/L in the 2nd~6th month of life, <60U/L in the 7th~12th month and <50U/L beyond one year.

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.