Deleterious Variants in ABCC12 are Detected in Idiopathic Chronic Cholestasis and Cause Intrahepatic Bile Duct Loss in Model Organisms.

BACKGROUND & AIMS: The etiology of cholestasis remains unknown in many children. We surveyed the genome of children with chronic cholestasis for variants in genes not previously associated with liver disease and validated their biological relevance in zebrafish and murine models. METHOD: Whole-exome (n = 4) and candidate gene sequencing (n = 89) was completed on 93 children with cholestasis and normal serum γ-glutamyl transferase (GGT) levels without pathogenic variants in genes known to cause low GGT cholestasis such as ABCB11 or ATP8B1. CRISPR (clustered regularly interspaced short palindromic repeats)/Cas9 genome editing was used to induce frameshift pathogenic variants in the candidate gene in zebrafish and mice. RESULTS: In a 1-year-old female patient with normal GGT cholestasis and bile duct paucity, we identified a homozygous truncating pathogenic variant (c.198delA, p.Gly67Alafs∗6) in the ABCC12 gene (NM_033226). Five additional rare ABCC12 variants, including a pathogenic one, were detected in our cohort. ABCC12 encodes multidrug resistance-associated protein 9 (MRP9) that belongs to the adenosine 5'-triphosphate-binding cassette transporter C family with unknown function and no previous implication in liver disease. Immunohistochemistry and Western blotting revealed conserved MRP9 protein expression in the bile ducts in human, mouse, and zebrafish. Zebrafish abcc12-null mutants were prone to cholangiocyte apoptosis, which caused progressive bile duct loss during the juvenile stage. MRP9-deficient mice had fewer well-formed interlobular bile ducts and higher serum alkaline phosphatase levels compared with wild-type mice. They exhibited aggravated cholangiocyte apoptosis, hyperbilirubinemia, and liver fibrosis upon cholic acid challenge. CONCLUSIONS: Our work connects MRP9 with bile duct homeostasis and cholestatic liver disease for the first time. It identifies a potential therapeutic target to attenuate bile acid-induced cholangiocyte injury.

Cholestasis Due to USP53 Deficiency.

OBJECTIVES: Although a number of genetic forms of cholestasis have been identified, the genetic etiology of disease remains unidentified in a subset of cholestasis patients. METHODS: Whole exome sequencing (WES) was performed in DNA from patients diagnosed with cholestasis, at different points on the continuum from progressive familial intrahepatic cholestasis to benign recurrent intrahepatic cholestasis, in whom no disease mutations in known cholestasis genes had been identified. Candidate genes were then assessed in a larger patient sample, by targeted next-generation sequencing (NGS). Disease features at presentation and follow-up were collected from available medical records. RESULTS: By WES, we identified 3 patients with homozygous mutations in USP53. Screening of USP53 in a larger set of patients identified 4 additional patients with homozygous mutations in USP53. Six of the 7 patients had deletion mutations, and 1 had a missense mutation; 3 of the patients were siblings, all bearing a deletion that also disrupted neighboring MYOZ2. Age of onset ranged from early infancy to adolescence. Cholestasis tended to be biochemically mild and intermittent, and responsive to medication. Liver fibrosis was, however, present in all 4 patients who were biopsied, and splenomegaly was apparent in 5 of 7 at last ultrasound. CONCLUSIONS: Two groups recently identified patients with liver disease and mutation in USP53. We have now identified biallelic mutation in USP53 in 7 further patients with cholestasis, from 5 families. Most individuals had evidence of chronic liver disease, and long-term follow-up is recommended.

Presentation and Outcomes of Infants With Idiopathic Cholestasis: A Multicenter Prospective Study.

OBJECTIVES: The aim of the study was to determine the frequency and natural history of infantile idiopathic cholestasis (IC) in a large, prospective, multicenter cohort of infants. METHODS: We studied 94 cholestatic infants enrolled up to 6 months of age in the NIDDK ChiLDReN (Childhood Liver Disease Research Network) "PROBE" protocol with a final diagnosis of IC; they were followed up to 30 months of age. RESULTS: Male sex (66/94; 70%), preterm birth (22/90 with data; 24% born at < 37 weeks' gestational age), and low birth weight (25/89; 28% born at <2500 g) were frequent, with no significant differences between outcomes. Clinical outcomes included death (n = 1), liver transplant (n = 1), biochemical resolution (total bilirubin [TB] ≤1 mg/dL and ALT < 35 U/L; n = 51), partial resolution (TB > 1 mg/dL and/or ALT > 35 U/L; n = 7), and exited healthy (resolved disease per study site report but without documented biochemical resolution; n = 34). Biochemical resolution occurred at median of 9 months of age. GGT was <100 U/L at baseline in 34 of 83 participants (41%). CONCLUSIONS: Frequency of IC and of death or liver transplant was less common in this cohort than in previously published cohorts, likely because of recent discovery and diagnosis of genetic etiologies of severe/persistent cholestasis that previously were labeled as idiopathic. Preterm birth and other factors associated with increased vulnerability in neonates are relatively frequent and may contribute to IC. Overall outcome in IC is excellent. Low/normal GGT was common, possibly indicating a role for variants in genes associated with low-GGT cholestasis-this warrants further study.

Mutation Analysis and Disease Features at Presentation in a Multi-Center Cohort of Children With Monogenic Cholestasis.

OBJECTIVES: To advance our understanding of monogenic forms of intrahepatic cholestasis. METHODS: Analyses included participants with pathogenic biallelic mutations in adenosine triphosphate (ATP)-binding cassette subfamily B member 11 (ABCB11) (bile salt export pump; BSEP) or adenosine triphosphatase (ATPase) phospholipid transporting 8B1 (ATP8B1) (familial intrahepatic cholestasis; FIC1), or those with monoallelic or biallelic mutations in adenosine triphosphate (ATP)-binding cassette subfamily B member 4 (ABCB4) (multidrug resistance; MDR3), prospectively enrolled in the Longitudinal Study of Genetic Causes of Intrahepatic Cholestasis (LOGIC; NCT00571272) between November 2007 and December 2013. Summary statistics were calculated to describe baseline demographics, history, anthropometrics, laboratory values, and mutation data. RESULTS: Ninety-eight participants with FIC1 (n = 26), BSEP (n = 53, including 8 with biallelic truncating mutations [severe] and 10 with p.E297G or p.D482G [mild]), or MDR3 (n = 19, including four monoallelic) deficiency were analyzed. Thirty-five had a surgical interruption of the enterohepatic circulation (sEHC), including 10 who underwent liver transplant (LT) after sEHC. Onset of symptoms occurred by age 2 years in most with FIC1 and BSEP deficiency, but was later and more variable for MDR3. Pruritus was nearly universal in FIC1 and BSEP deficiency. In participants with native liver, failure to thrive was common in FIC1 deficiency, high ALT was common in BSEP deficiency, and thrombocytopenia was common in MDR3 deficiency. sEHC was successful after more than 1 year in 7 of 19 participants with FIC1 and BSEP deficiency. History of LT was most common in BSEP deficiency. Of 102 mutations identified, 43 were not previously reported. CONCLUSIONS: In this cohort, BSEP deficiency appears to be correlated with a more severe disease course. Genotype-phenotype correlations in these diseases are not straightforward and will require the study of larger cohorts.

Identification of Polycystic Kidney Disease 1 Like 1 Gene Variants in Children With Biliary Atresia Splenic Malformation Syndrome.

Biliary atresia (BA) is the most common cause of end-stage liver disease in children and the primary indication for pediatric liver transplantation, yet underlying etiologies remain unknown. Approximately 10% of infants affected by BA exhibit various laterality defects (heterotaxy) including splenic abnormalities and complex cardiac malformations-a distinctive subgroup commonly referred to as the biliary atresia splenic malformation (BASM) syndrome. We hypothesized that genetic factors linking laterality features with the etiopathogenesis of BA in BASM patients could be identified through whole-exome sequencing (WES) of an affected cohort. DNA specimens from 67 BASM subjects, including 58 patient-parent trios, from the National Institute of Diabetes and Digestive and Kidney Diseases-supported Childhood Liver Disease Research Network (ChiLDReN) underwent WES. Candidate gene variants derived from a prespecified set of 2,016 genes associated with ciliary dysgenesis and/or dysfunction or cholestasis were prioritized according to pathogenicity, population frequency, and mode of inheritance. Five BASM subjects harbored rare and potentially deleterious biallelic variants in polycystic kidney disease 1 like 1 (PKD1L1), a gene associated with ciliary calcium signaling and embryonic laterality determination in fish, mice, and humans. Heterozygous PKD1L1 variants were found in 3 additional subjects. Immunohistochemical analysis of liver from the one BASM subject available revealed decreased PKD1L1 expression in bile duct epithelium when compared to normal livers and livers affected by other noncholestatic diseases. Conclusion: WES identified biallelic and heterozygous PKD1L1 variants of interest in 8 BASM subjects from the ChiLDReN data set; the dual roles for PKD1L1 in laterality determination and ciliary function suggest that PKD1L1 is a biologically plausible, cholangiocyte-expressed candidate gene for the BASM syndrome.

ATP11C targets basolateral bile salt transporter proteins in mouse central hepatocytes.

UNLABELLED: ATP11C is a homolog of ATP8B1, both of which catalyze the transport of phospholipids in biological membranes. Mutations in ATP8B1 cause progressive familial intrahepatic cholestasis type1 in humans, which is characterized by a canalicular cholestasis. Mice deficient in ATP11C are characterized by a conjugated hyperbilirubinemia and an unconjugated hypercholanemia. Here, we have studied the hypothesis that ATP11C deficiency interferes with basolateral uptake of unconjugated bile salts, a process mediated by organic anion-transporting polypeptide (OATP) 1B2. ATP11C localized to the basolateral membrane of central hepatocytes in the liver lobule of control mice. In ATP11C-deficient mice, plasma total bilirubin levels were 6-fold increased, compared to control, of which ∼65% was conjugated and ∼35% unconjugated. Plasma total bile salts were 10-fold increased and were mostly present as unconjugated species. Functional studies in ATP11C-deficient mice indicated that hepatic uptake of unconjugated bile salts was strongly impaired whereas uptake of conjugated bile salts was unaffected. Western blotting and immunofluorescence analysis demonstrated near absence of basolateral bile salt uptake transporters OATP1B2, OATP1A1, OATP1A4, and Na(+) -taurocholate-cotransporting polypeptide only in central hepatocytes of ATP11C-deficient liver. In vivo application of the proteasome inhibitor, bortezomib, partially restored expression of these proteins, but not their localization. Furthermore, we observed post-translational down-regulation of ATP11C protein in livers from cholestatic mice, which coincided with reduced OATP1B2 levels. CONCLUSIONS: ATP11C is essential for basolateral membrane localization of multiple bile salt transport proteins in central hepatocytes and may act as a gatekeeper to prevent hepatic bile salt overload. Conjugated hyperbilirubinemia and unconjugated hypercholanemia and loss of OATP expression in ATP11C-deficient liver strongly resemble the characteristics of Rotor syndrome, suggesting that mutations in ATP11C can predispose to Rotor syndrome. (Hepatology 2016;64:161-174).

Genetic defects in bile acid conjugation cause fat-soluble vitamin deficiency.

BACKGROUND & AIMS: The final step in bile acid synthesis involves conjugation with glycine and taurine, which promotes a high intraluminal micellar concentration to facilitate lipid absorption. We investigated the clinical, biochemical, molecular, and morphologic features of a genetic defect in bile acid conjugation in 10 pediatric patients with fat-soluble vitamin deficiency, some with growth failure or transient neonatal cholestatic hepatitis. METHODS: We identified the genetic defect that causes this disorder using mass spectrometry analysis of urine, bile, and serum samples and sequence analysis of the genes encoding bile acid-CoA:amino acid N-acyltransferase (BAAT) and bile acid-CoA ligase (SLC27A5). RESULTS: Levels of urinary bile acids were increased (432 ± 248 µmol/L) and predominantly excreted in unconjugated forms (79.4% ± 3.9%) and as sulfates and glucuronides. Glycine or taurine conjugates were absent in the urine, bile, and serum. Unconjugated bile acids accounted for 95.7% ± 5.8% of the bile acids in duodenal bile, with cholic acid accounting for 82.4% ± 5.5% of the total. Duodenal bile acid concentrations were 12.1 ± 5.9 mmol/L, which is too low for efficient lipid absorption. The biochemical profile was consistent with defective bile acid amidation. Molecular analysis of BAAT confirmed 4 different homozygous mutations in 8 patients tested. CONCLUSIONS: Based on a study of 10 pediatric patients, genetic defects that disrupt bile acid amidation cause fat-soluble vitamin deficiency and growth failure, indicating the importance of bile acid conjugation in lipid absorption. Some patients developed liver disease with features of a cholangiopathy. These findings indicate that patients with idiopathic neonatal cholestasis or later onset of unexplained fat-soluble vitamin deficiency should be screened for defects in bile acid conjugation.

Complex inheritance of familial hypercholanemia with associated mutations in TJP2 and BAAT.

Familial hypercholanemia (FHC) is characterized by elevated serum bile acid concentrations, itching, and fat malabsorption. We show here that FHC in Amish individuals is associated with mutations in tight junction protein 2 (encoded by TJP2, also known as ZO-2) and bile acid Coenzyme A: amino acid N-acyltransferase (encoded by BAAT). The mutation of TJP2, which occurs in the first PDZ domain, reduces domain stability and ligand binding in vitro. We noted a morphological change in hepatic tight junctions. The mutation of BAAT, a bile acid-conjugating enzyme, abrogates enzyme activity; serum of individuals homozygous with respect to this mutation contains only unconjugated bile acids. Mutations in both TJP2 and BAAT may disrupt bile acid transport and circulation. Inheritance seems to be oligogenic, with genotype at BAAT modifying penetrance in individuals homozygous with respect to the mutation in TJP2.

Liver Disease and Risk of Hepatocellular Carcinoma in Children With Mutations in TALDO1.

Mutations in the transaldolase 1 (TALDO1) gene have been described in a limited number of cases. Several organs can be affected and clinical manifestations are variable, but often include liver dysfunction and/or hepatosplenomegaly. We report 4 patients presenting with liver disease: 2 with early-onset hepatocellular carcinoma (HCC). Patients with cholestasis and mutations in TALDO1 were identified by next-generation sequencing. Clinical, laboratory, and histological data were collected. Four (1 male) patients were identified with variants predicted to be damaging in TALDO1. Three patients were homozygous (two protein truncating/one missense mutations), 1 one was compound heterozygous (two missense mutations). Median age at presentation was 4 months (range, 2-210 days) with jaundice (3), hepatosplenomegaly (3), and pancytopaenia (1). The diagnosis was corroborated by detection of minimal transaldolase enzyme activity in skin fibroblasts in two cases and raised urine polyols in the third. Three patients underwent liver transplantation (LT), 2 of whom had confirmed HCC on explanted liver. One patient suddenly died shortly after LT. The nontransplanted case has a chronic liver disease with multiple dysplastic liver nodules, but normal liver biochemistry and alpha-fetoprotein. Median follow-up was 4 years (range, 1-21). Conclusion: Transaldolase deficiency can include early-onset normal gamma-glutamyltransferase liver disease with multisystem involvement and variable progression. Patients with this disease are at risk of early-onset HCC and may require early LT.

Progressive familial intrahepatic cholestasis - farnesoid X receptor deficiency due to NR1H4 mutation: A case report.

BACKGROUND: Functioning farnesoid X receptor (FXR; encoded by NR1H4) is key to normal bile acid homeostasis. Biallelic mutations in NR1H4 are reported in a few children with intrahepatic cholestasis. We describe a boy with progressive familial intrahepatic cholestasis and homozygous mutation in NR1H4. CASE SUMMARY: A boy had severe neonatal cholestasis with moderate hypercholanemia and persistently elevated alpha-fetoprotein. Despite medical treatment, coagulopathy was uncontrollable, prompting liver transplantation at age 8 mo with incidental splenectomy. The patient experienced catch-up growth with good liver function and did not develop allograft steatosis. However, 1 year after transplant, he died from an acute infection, considered secondary to immunosuppression and asplenia. A homozygous protein-truncating mutation, c.547C > T, p.(Arg183Ter), was subsequently identified in NR1H4, and both parents were shown to be heterozygous carriers. Absence of FXR and of bile salt export pump expression was confirmed by immunostaining of explanted liver. CONCLUSION: Severe cholestasis with persistently high alpha-fetoprotein and modest elevation of serum bile acid levels may suggest FXR deficiency. Some patients with FXR deficiency may not develop allograft steatosis and may respond well to liver transplantation.

Differences in presentation and progression between severe FIC1 and BSEP deficiencies.

BACKGROUND & AIMS: Progressive familial intrahepatic cholestasis (PFIC) with normal serum levels of gamma-glutamyltranspeptidase can result from mutations in ATP8B1 (encoding familial intrahepatic cholestasis 1 [FIC1]) or ABCB11 (encoding bile salt export pump [BSEP]). We evaluated clinical and laboratory features of disease in patients diagnosed with PFIC, who carried mutations in ATP8B1 (FIC1 deficiency) or ABCB11 (BSEP deficiency). Our goal was to identify features that distinguish presentation and course of these two disorders, thus facilitating diagnosis and elucidating the differing consequences of ATP8B1 and ABCB11 mutations. METHODS: A retrospective multi-center study was conducted, using questionnaires and chart review. Available clinical and biochemical data from 145 PFIC patients with mutations in either ATP8B1 (61 "FIC1 patients") or ABCB11 (84 "BSEP patients") were evaluated. RESULTS: At presentation, serum aminotransferase and bile salt levels were higher in BSEP patients; serum alkaline phosphatase values were higher, and serum albumin values were lower, in FIC1 patients. Elevated white blood cell counts, and giant or multinucleate cells at liver biopsy, were more common in BSEP patients. BSEP patients more often had gallstones and portal hypertension. Diarrhea, pancreatic disease, rickets, pneumonia, abnormal sweat tests, hearing impairment, and poor growth were more common in FIC1 patients. Among BSEP patients, the course of disease was less rapidly progressive in patients bearing the D482G mutation. CONCLUSIONS: Severe forms of FIC1 and BSEP deficiency differed. BSEP patients manifested more severe hepatobiliary disease, while FIC1 patients showed greater evidence of extrahepatic disease.

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

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

Hereditary forms of intrahepatic cholestasis.

Several genes that are mutated in hereditary forms of intrahepatic cholestasis have been identified or mapped, providing new insights into the process of enterohepatic bile acid circulation in health and disease and new tools with which to study this process. Murine models of several of these disorders have been generated. Unanticipated genetic heterogeneity has been identified.

Bile composition in Alagille Syndrome and PFIC patients having Partial External Biliary Diversion.

BACKGROUND: Partial External Biliary Diversion (PEBD) is a surgical intervention to treat children with Progressive Familial Intrahepatic Cholestasis (PFIC) and Alagille syndrome (AGS). PEBD can reduce disease progression, and examining the alterations in biliary lipid composition may be a prognostic factor for outcome. METHODS: Biliary lipid composition and the clinical course of AGS and PFIC patients were examined before and after PEBD. RESULTS: Pre-PEBD bile from AGS patients had greater chenodeoxycholic/cholic acid (CDCA/CA), bile salt, cholesterol and phospholipid concentrations than PFIC patients. AGS patients, and PFIC patients with familial intrahepatic cholestasis 1 (FIC1) genotype, responded better to PEBD than PFIC patients with bile salt export protein (BSEP) genotype. After successful PEBD, AGS patients have higher biliary lipid concentrations than PFIC patients and PEBD also increases biliary phospholipid concentrations in FIC1 patients. CONCLUSION: Both AGS and FIC1 patients can benefit from PEBD, and preserved biliary phospholipid concentrations may be associated with better outcomes post-PEBD.

Progressive Familial Intrahepatic Cholestasis.

Genetic cholestasis has been dissected through genetic investigation. The major PFIC genes are now described. ATP8B1 encodes FIC1, ABCB11 encodes BSEP, ABCB4 encodes MDR3, TJP2 encodes TJP2, NR1H4 encodes FXR, and MYO5B encodes MYO5B. The full spectra of phenotypes associated with mutations in each gene are discussed, along with our understanding of the disease mechanisms. Differences in treatment response and targets for future treatment are emerging.

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

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

Intrahepatic Cholestasis of Pregnancy (ICP) in U.S. Latinas and Chileans: Clinical features, Ancestry Analysis, and Admixture Mapping.

In the Americas, women with Indigenous American ancestry are at increased risk of intrahepatic cholestasis of pregnancy (ICP), relative to women of other ethnicities. We hypothesized that ancestry-related genetic factors contribute to this increased risk. We collected clinical and laboratory data, and performed biochemical assays on samples from U.S. Latinas and Chilean women, with and without ICP. The study sample included 198 women with ICP (90 from California, U.S., and 108 from Chile) and 174 pregnant control women (69 from California, U.S., and 105 from Chile). SNP genotyping was performed using Affymetrix arrays. We compared overall genetic ancestry between cases and controls, and used a genome-wide admixture mapping approach to screen for ICP susceptibility loci. We identified commonalities and differences in features of ICP between the 2 countries and determined that cases had a greater proportion of Indigenous American ancestry than did controls (p = 0.034). We performed admixture mapping, taking country of origin into account, and identified one locus for which Native American ancestry was associated with increased risk of ICP at a genome-wide level of significance (P = 3.1 x 10(-5), Pcorrected = 0.035). This locus has an odds ratio of 4.48 (95% CI: 2.21-9.06) for 2 versus zero Indigenous American chromosomes. This locus lies on chromosome 2, with a 10 Mb 95% confidence interval which does not contain any previously identified hereditary 'cholestasis genes.' Our results indicate that genetic factors contribute to the risk of developing ICP in the Americas, and support the utility of clinical and genetic studies of ethnically mixed populations for increasing our understanding of ICP.

Mutations in TJP2 cause progressive cholestatic liver disease.

Elucidating genetic causes of cholestasis has proved to be important in understanding the physiology and pathophysiology of the liver. Here we show that protein-truncating mutations in the tight junction protein 2 gene (TJP2) cause failure of protein localization and disruption of tight-junction structure, leading to severe cholestatic liver disease. These findings contrast with those in the embryonic-lethal knockout mouse, highlighting differences in redundancy in junctional complexes between organs and species.