Parental mosaicism of JAG1 mutations in families with Alagille syndrome

A case of infantile Alagille syndrome with severe dyslipidemia: a new insight into lipid metabolism and therapeutics

Alagille syndrome (AGS) is an autosomal dominant genetic disorder characterized by congenital heart disease, hepatic cholestasis, dyslipidemia, and characteristic facies since infancy. Cholestatic hypercholesterolemia in patients diagnosed with AGS is occasionally refractory and resistant to conventional treatments. We report the case of a 4-month-old boy diagnosed with AGS and refractory dyslipidemia due to cholestatic liver disease. He had repeated episodes of cyanosis due to pulmonary artery atresia since birth and underwent a Blalock-Taussig shunt procedure at age 3 months. At age 4 months, cholestatic hyperbilirubinemia deteriorated to a serum total bilirubin level of 19.9 mg/dL. At age 12 months, a laboratory test revealed severe dyslipidemia (serum total cholesterol, 1796 mg/dL; serum triglycerides [TGs], 635 mg/dL), and the presence of xanthomas. A pathogenic variant of the JAG1 gene (c.1326G > A, p.Trp442X) was detected through genetic testing. Oral ursodeoxycholate normalized hyperbilirubinemia with a subtle improvement in dyslipidemia. Combination therapy with pravastatin and fenofibrate did not successfully improve dyslipidemia. At age 20 months, altering pravastatin to atorvastatin was effective in normalizing serum cholesterol and TGs with no adverse events.

Combination therapy with atorvastatin and fenofibrate was successful in improving refractory dyslipidemia in a child with AGS. Atorvastatin is a well-known strong statin that can lower serum cholesterol, and fenofibrate can lower serum TG levels. We propose that atorvastatin be taken into consideration for the treatment of persistent hyperlipidemia in patients diagnosed with AGS, because atorvastatin upregulates bile acid synthesis and lipoprotein scavenging, and inhibits intrinsic cholesterol production.

Alagille syndrome and risk for hepatocellular carcinoma: Need for increased surveillance in adults with mild liver phenotypes

Alagille syndrome (ALGS) is a multisystem autosomal dominant developmental disorder caused predominantly by pathogenic variants in JAGGED1 (JAG1), and also by pathogenic variants in NOTCH2 in a much smaller number of individuals. Clinical presentation is highly variable and includes liver, heart, eye, skeleton, and facial abnormalities, with a subset of individuals also presenting with kidney, vascular, and central nervous system phenotypes. Hepatocellular carcinoma (HCC) is a rare complication of ALGS, though little is known about its incidence or etiology among affected individuals. Previous reports have identified HCC occurrence in both pediatric and adult cases of ALGS. We present a case report of HCC in a 58‐year‐old woman with a pathogenic JAG1 variant and no overt hepatic features of ALGS. Through a comprehensive literature review, we compile all reported pediatric and adult cases, and further highlight one previously reported case of HCC onset in an adult ALGS patient without any hepatic disease features, similar to our own described patient. Our case report and literature review suggest that ALGS‐causing variants could confer risk for developing HCC regardless of phenotypic severity and highlight a need for a cancer screening protocol that would enable early detection and treatment in this at‐risk population.

Targeted Sequencing and RNA Assay Reveal a Noncanonical JAG1 Splicing Variant Causing Alagille Syndrome

Alagille syndrome (ALGS), as known as congenital arteriohepatic dysplasia, is a rare autosomal dominant multi-systemic disorder. Mutations in JAG1 or more rarely NOTCH2 have been reported as the cause of ALGS. In this study, a 5-year old girl with typical ALGS feature and her pregnant mother came to our reproductive genetics clinic for counseling. We aimed to clarify the genetic diagnosis and provide prenatal genetic diagnosis for the pregnant. Next generation sequencing (NGS)-based multigene panel was used to identify pathogenic variant of the proband. Then the candidate variant was verified by using Sanger sequencing. RNA assay was performed to clarify splicing effect of the candidate variant. Amniocentesis, karyotyping, and Sanger sequencing were performed for prenatal testing. We found a novel de novo noncanonical JAG1 splicing variant (c.2917-8C > A) in the proband. Peripheral blood RNA assay suggested that the mutant transcript might escape nonsense-mediated messenger RNA (mRNA) decay (NMD) and encode a C-terminal truncated protein. Information of the variant has resulted in a successful prenatal diagnosis of the fetus. Our results clarified the genetic diagnosis of an ALGS patient and ensured utility of prenatal genetic testing.

Alagille syndrome mutation update: Comprehensive overview of JAG1 and NOTCH2 mutation frequencies and insight into missense variant classification

Alagille syndrome is an autosomal dominant disease with a known molecular etiology of dysfunctional Notch signaling caused primarily by pathogenic variants in JAGGED1 (JAG1), but also by variants in NOTCH2. The majority of JAG1 variants result in loss of function, however disease has also been attributed to lesser understood missense variants. Conversely, the majority of NOTCH2 variants are missense, though fewer of these variants have been described. In addition, there is a small group of patients with a clear clinical phenotype in the absence of a pathogenic variant. Here, we catalog our single-center study, which includes 401 probands and 111 affected family members amassed over a 27-year period, to provide updated mutation frequencies in JAG1 and NOTCH2 as well as functional validation of nine missense variants. Combining our cohort of 86 novel JAG1 and three novel NOTCH2 variants with previously published data (totaling 713 variants), we present the most comprehensive pathogenic variant overview for Alagille syndrome. Using this data set, we developed new guidance to help with the classification of JAG1 missense variants. Finally, we report clinically consistent cases for which a molecular etiology has not been identified and discuss the potential for next generation sequencing methodologies in novel variant discovery.

JAG1 loss‑of‑function mutations contributed to Alagille syndrome in two Chinese families

Alagille syndrome (ALGS) is primarily caused by jagged1 (JAG1) mutations, 70% of which are protein‑truncating mutations. However, no mutation hotspots have been discovered, and the pathogenic mechanism is not fully understood. The aim of the present study was to analyze two protein‑truncating JAG1 mutations detected in three Chinese ALGS patients. Mutation c.1261delT (p.Cys421Valfs) was identified in one patient with hepatic damage, xanthomas, facial abnormalities and cardiovascular defects, which was inherited from his father. The other mutation, c.1382_1383delAC (p.Asp461Glyfs), carried by a pair of monozygotic twins with hepatic damage, facial abnormalities and cardiovascular defects, was de novo. Biological experiments were performed to study the characteristics and function of these mutations. The p.Cys421Valfs and p.Asp461Glyfs mutant proteins appeared to be truncated in western blotting using anti‑Flag bound to the N‑terminus of JAG1. The RBP‑Jκ‑responsive reporter gene assay was used to investigate the ability of mutant JAG1 proteins to activate the Notch signaling pathway. The mutant proteins had a lower luciferase activity than the wild‑type, indicating impaired transcriptional activation ability. Western blotting using soluble JAG1 from the culture medium revealed that the expression levels of the mutant proteins were lower than that of the wild‑type, suggesting that less mutant JAG1 protein underwent proteolytic cleavage than the wild‑type. In conclusion, these two loss‑of‑function JAG1 mutations may be associated with ALGS manifestations in these patients.

Combined genetic analyses can achieve efficient diagnostic yields for subjects with Alagille syndrome and incomplete Alagille syndrome

AIM

We evaluated combined genetic analyses with targeted next-generation sequencing (NGS), multiplex ligation probe amplification (MLPA) of Jagged1 (JAG1) genes and microarray comparative genomic hybridisation (CGH) in subjects with Alagille syndrome, incomplete clinical features of Alagille syndrome and biliary atresia.

METHODS

Subjects recruited from April 2013 to December 2015 underwent a targeted NGS analysis, including JAG1 and Notch homolog 2 (NOTCH2). If no mutations were detected in JAG1 or NOTCH2, or if copy number variations were suggested by the NGS analysis, we performed an MLPA analysis of JAG1. We also performed a microarray CGH analysis with whole-exon deletion detected by the MLPA analysis.

RESULTS

We analysed 30 subjects with Alagille syndrome, nine with incomplete Alagille syndrome and 17 with biliary atresia and detected pathogenic mutations in JAG1 or NOTCH2 in 24/30 subjects with Alagille syndrome and in 4/9 subjects with incomplete Alagille syndrome. No pathogenic mutations were detected in subjects with biliary atresia. The frequency of JAG1 mutations was as follows: single nucleotide variants (51.9%), small insertion or deletion (29.6%) and gross deletion (18.5%).

CONCLUSION

Combined genetic analyses achieved efficient diagnostic yields for subjects with Alagille syndrome and incomplete Alagille syndrome.

Alagille syndrome: clinical perspectives

Alagille syndrome is an autosomal dominant, complex multisystem disorder characterized by the presence of three out of five major clinical criteria: cholestasis with bile duct paucity on liver biopsy, congenital cardiac defects (with particular involvement of the pulmonary arteries), posterior embryotoxon in the eye, characteristic facial features, and butterfly vertebrae. Renal and vascular abnormalities can also occur. Inter- and intrafamilial variabilities in the clinical manifestations are common. We reviewed the clinical features and management as well as the molecular basis of Alagille syndrome.

JAG1 Mutation Spectrum and Origin in Chinese Children with Clinical Features of Alagille Syndrome

Alagille syndrome is an autosomal dominant disorder that results from defects in the Notch signaling pathway, which is most frequently due to JAG1 mutations. This study investigated the rate, spectrum, and origin of JAG1 mutations in 91 Chinese children presenting with at least two clinical features of Alagille syndrome (cholestasis, heart murmur, skeletal abnormalities, ocular abnormalities, characteristic facial features, and renal abnormalities). Direct sequencing and/or multiplex-ligation-dependent probe amplification were performed in these patients, and segregation analysis was performed using samples available from the parents. JAG1 disease-causing mutations were detected in 70/91 (76.9%) patients, including 29/70 (41.4%) small deletions, 6/70 (8.6%) small insertions, 16/70 (22.9%) nonsense mutations, 8/70 (11.4%) splice-site mutations, 6/70 (9.4%) missense mutations, and 5/70 (7.1%) gross deletions. Of the mutations detected, 45/62 (72.6%) were novel, and almost all were unique, with the exception of c.439C>T, c.439+1G>A, c.703C>T, c.1382_1383delAC, c.2698C>T, and c.2990C>A, which were detected in two cases each; three cases exhibited entire gene deletions. A majority (69.2%) of the point and frameshift mutations could be detected by the sequencing of eleven exons (exons 3, 5, 6, 11, 14, 16, 18, 21, and 23-25). The mutation detection rate was 50.0% (10/20) in atypical cases that only presented with two or three clinical features of Alagille syndrome. Segregation analysis revealed that 81.1% (30/37) of these mutations were de novo. In conclusion, JAG1 mutations are present in the majority of Chinese pediatric patients with clinical features of Alagille syndrome, and the mutations concentrate on different exons from other reports. Genetic study is important for the diagnosis of atypical Alagille syndrome in Chinese patients.

Spectrum of JAG1 gene mutations in Polish patients with Alagille syndrome

Alagille syndrome (ALGS) is an autosomal dominant disorder characterized by developmental abnormalities in several organs including the liver, heart, eyes, vertebrae, kidneys, and face. The majority (90-94 %) of ALGS cases are caused by mutations in the JAG1 (JAGGED1) gene, and in a small percent of patients (∼1 %) mutations in the NOTCH2 gene have been described. Both genes are involved in the Notch signaling pathway. To date, over 440 different JAG1 gene mutations and ten NOTCH2 mutations have been identified in ALGS patients. The present study was conducted on a group of 35 Polish ALGS patients and revealed JAG1 gene mutations in 26 of them. Twenty-three different mutations were detected including 13 novel point mutations and six large deletions affecting the JAG1 gene. Review of all mutations identified to date in individuals from Poland allowed us to propose an effective diagnostic strategy based on the mutations identified in the reported patients of Polish descent. However, the distribution of mutations seen in this cohort was not substantively different than the mutation distribution in other reported populations.

Alagille syndrome in a Vietnamese cohort: mutation analysis and assessment of facial features

Alagille syndrome (ALGS, OMIM #118450) is an autosomal dominant disorder that affects multiple organ systems including the liver, heart, eyes, vertebrae, and face. ALGS is caused by mutations in one of two genes in the Notch Signaling Pathway, Jagged1 (JAG1) or NOTCH2. In this study, analysis of 21 Vietnamese ALGS individuals led to the identification of 19 different mutations (18 JAG1 and 1 NOTCH2), 17 of which are novel, including the third reported NOTCH2 mutation in Alagille Syndrome. The spectrum of JAG1 mutations in the Vietnamese patients is similar to that previously reported, including nine frameshift, three missense, two splice site, one nonsense, two whole gene, and one partial gene deletion. The missense mutations are all likely to be disease causing, as two are loss of cysteines (C22R and C78G) and the third creates a cryptic splice site in exon 9 (G386R). No correlation between genotype and phenotype was observed. Assessment of clinical phenotype revealed that skeletal manifestations occur with a higher frequency than in previously reported Alagille cohorts. Facial features were difficult to assess and a Vietnamese pediatric gastroenterologist was only able to identify the facial phenotype in 61% of the cohort. To assess the agreement among North American dysmorphologists at detecting the presence of ALGS facial features in the Vietnamese patients, 37 clinical dysmorphologists evaluated a photographic panel of 20 Vietnamese children with and without ALGS. The dysmorphologists were unable to identify the individuals with ALGS in the majority of cases, suggesting that evaluation of facial features should not be used in the diagnosis of ALGS in this population. This is the first report of mutations and phenotypic spectrum of ALGS in a Vietnamese population.

Alagille syndrome: pathogenesis, diagnosis and management

Alagille syndrome (ALGS), also known as arteriohepatic dysplasia, is a multisystem disorder due to defects in components of the Notch signalling pathway, most commonly due to mutation in JAG1 (ALGS type 1), but in a small proportion of cases mutation in NOTCH2 (ALGS type 2). The main clinical and pathological features are chronic cholestasis due to paucity of intrahepatic bile ducts, peripheral pulmonary artery stenosis, minor vertebral segmentation anomalies, characteristic facies, posterior embryotoxon/anterior segment abnormalities, pigmentary retinopathy, and dysplastic kidneys. It follows autosomal dominant inheritance, but reduced penetrance and variable expression are common in this disorder, and somatic/germline mosaicism may also be relatively frequent. This review discusses the clinical features of ALGS, including long-term complications, the clinical and molecular diagnosis, and management.

Screening for Alagille syndrome mutations in the JAG1 and NOTCH2 genes using denaturing high-performance liquid chromatography

Mutations in the JAG1 gene and the NOTCH2 gene cause Alagille syndrome. At present, however, genetic testing of Alagille syndrome is not commonly applied in clinical settings because the currently available assays are technically and financially demanding, mainly because of the size of the genes. In the present study, we optimized the highly sensitive and specific mutation scanning method automated denaturing high-performance liquid chromatography (DHPLC) to analyze the entire coding region of JAG1 and NOTCH2. The coding region was amplified by 69 primer pairs, all of which have the same cycling conditions, aliquoted on a 96-well format PCR plate. In this manner, all the exons were simultaneously amplified using a single block in a thermal cycler. We then wrote a computer script to analyze each segment of JAG1 and NOTCH2 by DHPLC in a serial manner using conditions that were optimized for each amplicon. The implementation of this screening method for JAG1 and NOTCH2 will help medical geneticists confirm their clinical impressions and provide accurate genetic counseling to the patients with Alagille syndrome and their families.

Prenatal molecular diagnosis of inherited cholestatic diseases

OBJECTIVES

Progressive familial intrahepatic cholestasis (PFIC) and to a lesser extent, Alagille syndrome, often lead to end-stage liver disease during childhood. We report our experience of DNA-based prenatal diagnosis of PFIC1-3 and Alagille syndrome.

PATIENTS AND METHODS

Four molecular antenatal diagnoses were performed in 3 PFIC families and 17 in 11 Alagille syndrome families. DNA was isolated from chorionic villus or cultured amniocyte samples from women, without pregnancy complications.

RESULTS

All four foetuses with a family history of PFIC1, 2, or 3 were heterozygous for an ATP8B1, ABCB11, or ABCB4 mutation and pregnancies were continued. Three of the infants were healthy after birth, and 1 premature infant, who had an ABCB4 mutation, experienced transient neonatal cholestasis. Among the families with a history of de novo JAG1 mutation, none of the foetuses was mutated, versus 40% of those with a history of familial mutation. Of 4 pregnant women with a JAG1-mutated foetus, 3 cut short their pregnancy and 1 gave birth to a child with overt Alagille syndrome.

CONCLUSIONS

Molecular antenatal diagnosis of PFIC1-3 and Alagille syndrome is reliable because clinical outcome after birth corresponded to molecular foetal data.

Peripheral Bile Duct Paucity and Cholestasis in the Liver of a Patient With Alagille Syndrome

Alagille syndrome (AGS) is a developmental, multiorgan disease caused by mutations of the Jagged1 gene. The liver is one of the major organs affected in AGS, and the hallmark of liver pathology in AGS is an age-related increase in the proportion of portal tracts that have no bile duct, but without evidence of prominent bile duct damage. The pathogenesis of this bile duct paucity is currently not well understood. (Immuno)histochemical and molecular analyses were performed on several liver biopsies that were taken during macroscopic examination of the explant liver of a 17-year-old AGS patient. The liver periphery was macroscopically pale and was microscopically characterized by complete absence of bile ducts and presence of severe cholestasis, but there was no ductular reaction. Conversely, the central, hilar portion contained normally developed bile ducts showing no or minimal damage and cholestasis. A missense mutation in the Jagged1 gene was present in both parts of the liver, indicating that mosaicism did not cause this peculiar picture. There was also a hypertrophy of the hepatic arterial branches in the liver periphery. Together with previous indirect findings, the current study of the explant liver of an AGS patient strongly suggests that a lack of branching and elongation of bile ducts during postnatal liver growth is the mechanism by which peripheral bile duct paucity and cholestasis develops in AGS. Our findings also suggest that anomalies of the intrahepatic arterial branches may be part of AGS in some patients.

Expression of mutant JAGGED1 alleles in patients with Alagille syndrome

Heterozygous mutations in JAGGED1 (JAG1), encoding a ligand for Notch receptors, have been identified in patients with Alagille syndrome (AGS). These mutations map to the extracellular and transmembrane domains of JAG1, giving rise in 70% cases to a premature termination codon (PTC). Although haploinsufficiency has been hypothesised as the main mechanism of AGS, a dominant negative effect of truncated forms of Serrate/Jagged has been suggested. Only few studies of the mutant mRNAs and proteins from AGS patients have been performed to elucidate the molecular mechanisms of the disease. To gain insight into the stability of mutant mRNAs, we studied transcripts from five livers and 24 lymphoblastoid cell lines (LCLs) of AGS patients. Mutant JAG1 transcripts were recovered (albeit in different relative amounts) from RNAs with missense mutations (five) or in-frame deletions (two), and from all but two of the 21 with PTCs. In addition, results from LCL RNAs correlated well with results from liver RNAs. Mutant transcripts were also recovered from tissues of a 23-week-old AGS foetus with a PTC mutation. This suggests that most mutant transcripts with PTCs escape nonsense-mediated mRNA decay (NMD) and could lead to the synthesis of soluble forms of JAG1. Production of a truncated protein was indeed observed after transfection of COS cells with a mutant JAG1 cDNA. In conclusion, mutant JAG1 transcripts are present in LCLs, livers and tissues of AGS patients, whatever the mutation type, and mutant proteins can be produced, suggesting a dominant negative effect of some mutant proteins as another molecular mechanism of AGS.

Phenotypic variability in Hey2 ?/? mice and absence of HEY2 mutations in patients with congenital heart defects or Alagille syndrome

The genetic alterations leading to congenital heart defects (CHD) are still poorly understood. We and others have recently shown that in mice loss of Hey2 results in a high incidence of fatal ventricular and atrial septal defects, combined with tricuspid stenosis or atresia in some cases. The phenotype has been postulated to resemble human tetralogy of Fallot. Our analysis of CD1 outbred mice suggests that phenotypic consequences of Hey2 loss can be quite variable and dependent on modifier genes as we detected only isolated VSDs with lower prevalence and a significantly reduced mortality rate in this strain. Since Hey2 is one of the few Notch target genes, it is also conceivable that HEY2 mutations may account for cases of Alagille syndrome (AGS: variable combinations of heart, skeleton, eye, and facial malformations and cholestasis), in which the typical mutations of the Notch ligand JAG1 cannot be found. To clarify the role of HEY2 in human CHD and AGS, we screened by direct sequencing 23 children with CHD and 38 patients diagnosed with AGS, which lack mutations in the JAG1 gene. We found two types of silent changes in the coding region: a CTT-->CTG transition in exon 3 and a CTG-->CTC polymorphism in exon 5. Furthermore, a heterozygous SNP in the splice donor site of exon 4 was detected that is unlikely to disrupt splicing. Although the high incidence and variability of human congenital heart defects implies a multifactorial genetic basis, our results suggest that mutation of HEY2 is not a major contributing factor.

Living-related liver transplantation for Alagille syndrome

Alagille syndrome (AGS) is an autosomal dominant genetic disorder characterized by chronic cholestasis, congenital heart disease, peculiar facies, butterfly-like vertebrae, and posterior embryotoxon. Liver dysfunction is the common presentation of AGS, and liver transplantation may be indicated. This study examines the outcome of living-related liver transplantation (LRLT) for AGS. Twenty patients with AGS (median age 5.0 years, range 0.6-12.9) underwent LRLT at Kyoto University Hospital between June 1990 and February 2002. Five potential donors were excluded because of paucity of intrahepatic bile ducts diagnosed by preoperative liver biopsy and one because of a hepatic vascular anomaly. The overall 5-year patient survival was 80.4%. Three patients died as the result of the following: complications related to surgery, heart failure caused by progressive pulmonary artery stenosis, and a graft with unsuspected bile duct paucity. Liver dysfunction was improved in all successful cases, and catch-up growth occurred in 90% of patients. LRLT is an efficacious treatment modality for AGS if donors are selected by cautious evaluation to rule out unsuspected bile duct paucity.

Alagille syndrome

Alagille syndrome (AGS) was described more than 35 years ago as a genetic entity characterised by five major features: chronic cholestasis owing to paucity of interlobular bile ducts; peripheral pulmonary stenosis; butterfly like vertebral arch defect; posterior embryotoxon and peculiar facies. AGS has long been said to have a relative good prognosis but overall survival at twenty years averages 70%. Complex congenital heart disease and hepatic disease with or without liver transplantation contribute significantly to mortality. JAGGED1 has been identified as a responsible gene by demonstration of mutations in AGS patients. Studies of JAGGED1 expression pattern demonstrate that minor features and almost all the elements in the long list of manifestations described in AGS patients are not coincidental. This suggests that Alagille syndrome definition may be revisited in the light of JAGGED1 mutations.

Familial deafness, congenital heart defects, and posterior embryotoxon caused by cysteine substitution in the first epidermal-growth-factor-like domain of jagged 1

In the present study, we report a kindred with hearing loss, congenital heart defects, and posterior embryotoxon, segregating as autosomal dominant traits. Six of seven available affected patients manifested mild-to-severe combined hearing loss, predominantly affecting middle frequencies. Two patients were diagnosed with vestibular pathology. All patients had congenital heart defects, including tetralogy of Fallot, ventricular septal defect, or isolated peripheral pulmonic stenosis. No individual in this family met diagnostic criteria for any previously described clinical syndrome. A candidate-gene approach was undertaken and culminated in the identification of a novel Jagged 1 (JAG1) missense mutation (C234Y) in the first cysteine of the first epidermal-growth-factor-like repeat domain of the protein. JAG1 is a cell-surface ligand in the Notch signaling pathway. Mutations in JAG1 have been identified in patients with Alagille syndrome. Our findings revealed a unique phenotype with highly penetrant deafness, posterior embryotoxon, and congenital heart defects but with variable expressivity in a large kindred, which demonstrates that mutation in JAG1 can cause hearing loss.

Cholestatic syndromes

Further insights into the molecular regulation of bile acid transport and metabolism have provided the basis for a better understanding of the pathogenesis of cholestatic liver diseases. Novel insights into the mechanisms of action of ursodeoxycholic acid should advance our understanding of the treatment of cholestatic liver diseases. Mutations of transporter genes can cause hereditary cholestatic syndromes in both infants and adults as well as cholesterol gallstone disease. Important studies have been published on the pathogenesis, clinical features, and treatment of primary biliary cirrhosis, drug-induced cholestasis, and cholestasis of pregnancy.