Mutations In JAG1 Research Articles

Vascular anomalies in Alagille syndrome: a significant cause of morbidity and mortality.

Alagille syndrome (AGS) is a dominantly inherited multisystem disorder involving the liver, heart, eyes, face, and skeleton, caused by mutations in Jagged1. Intracranial bleeding is a recognized complication and cause of mortality in AGS. There are multiple case reports of intracranial vessel abnormalities and other vascular anomalies in AGS. The objective of this study was to characterize the nature and spectrum of vascular anomalies in AGS. Retrospective chart review of 268 individuals with AGS was performed. Twenty-five patients (9%) had noncardiac vascular anomalies or events. Sixteen patients had documented structural vascular abnormalities. Two had basilar artery aneurysms, 7 had internal carotid artery anomalies, and another had a middle cerebral artery aneurysm. Moyamoya disease was described in 1 patient. Three of the 16 patients had aortic aneurysms, and 2 had aortic coarctations. One of the patients with a basilar artery aneurysm also had coarctation of the aorta. One of the individuals with an internal carotid artery anomaly also had renal artery stenosis. Nine more patients had intracranial events without documented vessel abnormalities. Vascular accidents accounted for 34% of the mortality in this cohort. The vascular anomalies described in our cohort of AGS individuals identify an underrecognized and potentially devastating complication of this disorder. It is a major cause of morbidity and mortality in this population, accounting for 34% of the mortality. We have also reviewed the body of evidence supporting a role for Jagged1 and the Notch signaling pathway in vascular development.

Molecular basis of intrahepatic cholestasis

Intrahepatic cholestasis, or impairment of bile flow, is an important manifestation of inherited and acquired liver disease. In recent years, human genetic and molecular studies have identified several genes, the disruption of which results in cholestasis. ATP8B1 (FIC1), ABCB11 (BSEP), and ABCB4 (MDR3) are disrupted in forms of progressive familial intrahepatic cholestasis (PFIC) and related disorders. Mutations in BAAT, TJP2 (ZO‐2), and EPHX1 have been identified in patients with hypercholanemia. A CLDN1 mutation was recently reported in patients with ichthyosis, leukocyte vacuoles, alopecia and sclerosing cholangitis (ILVASC), and North American Indian childhood cirrhosis (NAIC) is associated with a missense mutation in CIRH1A. Alagille syndrome patients carry mutations in JAG1, and mutations in VPS33B have been identified in patients with arthrogryposis, renal dysfunction and cholestasis syndrome (ARC). Identification of these genes, and characterization of the proteins they encode, is enhancing our understanding of the biology of the enterohepatic circulation in health and disease.

Conversion of biliary system to pancreatic tissue in Hes1-deficient mice.

The biliary system, pancreas and liver all develop from the nearby foregut at almost the same time in mammals. The molecular mechanisms that determine the identity of each organ in this complex area are unknown. Hes1 encodes the basic helix-loop-helix protein Hes1 (ref. 1), which represses positive basic helix-loop-helix genes such as Neurog3 (ref. 3). Expression of Hes1 is controlled by the evolutionarily conserved Notch pathway. Hes1 operates as a general negative regulator of endodermal endocrine differentiation, and defects in Notch signaling lead to accelerated pancreatic endocrine differentiation. Mutations in JAG1, encoding a Notch ligand, cause the Alagille syndrome in humans, characterized by poor development of the biliary system, suggesting that the Notch pathway is also involved in normal biliary development. Here we show that Hes1 is expressed in the extrahepatic biliary epithelium throughout development and that Hes1-deficient mice have gallbladder agenesis and severe hypoplasia of extrahepatic bile ducts. Biliary epithelium in Hes1-/- mice ectopically expresses the proendocrine gene Neurog3 (refs. 12,13), differentiates into endocrine and exocrine cells and forms acini and islet-like structures in the mutant bile ducts. Thus, biliary epithelium has the potential for pancreatic differentiation and Hes1 determines biliary organogenesis by preventing the pancreatic differentiation program, probably by directly repressing transcription of Neurog3.

Consequences of JAG1 mutations

Background: Alagille syndrome (AGS) is a multi-system, autosomal dominant disorder with highly variable expressivity, caused by mutations within the Jagged1 (JAG1) gene. Methods: We studied 53 mutation positive relatives of...

Conditional JAG1 Mutation Shows the Developing Heart Is More Sensitive Than Developing Liver to JAG1 Dosage

Mutations of Jagged 1 (JAG1), a ligand in the Notch signaling pathway, cause Alagille syndrome (AGS). AGS is an autosomal dominant, multisystem disorder with variable expressivity, characterized by bile duct paucity and resultant liver disease in combination with cardiac, ocular, skeletal, and facial findings. JAG1 mutations in AGS include gene deletions and protein truncating, splicing, and missense mutations, suggesting that haploinsufficiency is the mechanism of disease causation. With limited exceptions, there is no genotype-phenotype correlation. We have studied a JAG1 missense mutation (JAG1-G274D) that was previously identified in 13 individuals from an extended family with cardiac defects of the type seen in patients with AGS (e.g., peripheral pulmonic stenosis and tetralogy of Fallot) in the absence of liver dysfunction. Our data indicate that this mutation is "leaky." Two populations of proteins are produced from this allele. One population is abnormally glycosylated and is retained intracellularly rather than being transported to the cell surface. A second population is normally glycosylated and is transported to the cell surface, where it is able to signal to the Notch receptor. The JAG1-G274D protein is temperature sensitive, with more abnormally glycosylated (and nonfunctional) molecules produced at higher temperatures. Carriers of this mutation therefore have >50% but <100% of the normal concentration of JAG1 molecules on the cell surface. The cardiac-specific phenotype associated with this mutation suggests that the developing heart is more sensitive than the developing liver to decreased dosage of JAG1.

Bleeding tendency in children with Alagille syndrome.

Spontaneous intracranial bleeding is now a widely recognized complication and cause of mortality in patients with Alagille syndrome. The pathogenesis of intracranial bleeding in these patients remains unclear. The aim of the study was to look for other sites of bleeding in these patients that could suggest a factor of multiorgan morbidity. The records of 174 patients with Alagille syndrome were reviewed, and 38 (22%) patients without liver failure who experienced hemorrhage that led to a drop in hemoglobin level of at least 3 g/dL or to blood transfusion were identified. In 38 patients, 49 bleeding episodes occurred at a median age of 3.75 years (range: 1 month-27 years). Seventeen patients had 23 episodes of spontaneous bleeding; 21 patients bled during surgery or other medical procedures, and 5 among these 21 patients also had a spontaneous bleeding episode. Nine patients bled at least twice. Median platelets count and prothrombin time were normal. Severe cholestasis existed in 33 patients. One patient has a deletion of the 20p12 region, and 13 of 17 patients studied have a JAGGED1 mutation. Blood transfusion was necessary in 23 patients. Eight patients died secondary to bleeding (4 after surgery, 2 after gastrointestinal bleeding, 1 after needle liver biopsy, and 1 after intracranial bleeding). These results suggest that patients with Alagille syndrome are at special risk for bleeding; this should be taken into account before deciding on an invasive procedure. The mechanism of the bleeding is still unclear; the role of hypercholesterolemia cannot be excluded, but it may be speculated that JAGGED1 signaling abnormalities may impair the hemostatic function.

Identification of 36 novel Jagged1 (JAG1) mutations in patients with Alagille syndrome.

Alagille syndrome (AGS) is an autosomal dominant disorder characterized by five major symptoms: cholestasis, vertebral deformity, heart malformations, ocular defects and peculiar facial appearance. The previously described Jagged1 (JAG1) gene on chromosome 20p12 has been identified as being responsible for AGS. JAG1 encodes a transmembrane protein acting as ligand for the evolutionarily conserved Notch signaling pathway. Here we report 36 novel mutations in the JAG1 gene. We identified 12 novel deletions, 4 insertions, 8 missense, 7 nonsense and 5 splice site mutations. All mutations map to the sequence encoding the extracellular part of the Jagged1 protein. The mutations spread over the entire gene with slightly increased rates in exons 2 to 6 and exon 23 and 24. Eight novel missense mutations map to the Delta-Serrate-Lag2 (DSL) domain and adjacent sequences which are important for ligand-receptor interaction. Inheritance was determined in 27 families. Sixteen mutations (55%) were de novo and eleven mutations (45%) were transmitted. Altogether 226 different JAG1 mutations have been described in association with AGS, including our novel 36 mutations. AGS variants are spread over the entire gene with only a few mutations in exon 26. A relatively high number of mutations are clustered in exons 2 to 6. This sequence region shows high interspecies conservation and encodes the Notch receptor-binding region (DSL domain).

DHPLC mutation analysis of Jagged1 (JAG1) reveals six novel mutations in Australian alagille syndrome patients.

Alagille syndrome (AGS) is an autosomal dominant disorder characterized by abnormal development of the liver, heart, skeleton, eye, and face. Mutations in the Jagged1 gene have been found to result in the AGS phenotype. Using denaturing high performance liquid chromatography (DHPLC) mutation analysis we have screened 20 individuals with symptoms of AGS from 14 families for mutations within Jagged1. Eleven distinct Jagged1 mutations, six of which are novel, were identified in the 14 probands and affected family members. The mutations include four small deletions (36.6%), one small insertion (9.1%), three missense mutations (27.3%), one nonsense mutation (9.1%) and two splice donor site mutations (18.2%). The two newly identified splice site mutations were shown to cause the aberrant splicing of Jagged1 mRNA resulting in premature truncation of JAG1. A splice acceptor site mutation previously identified by our group in intron 13 was also shown to cause multiple splicing abnormalities of Jagged1 mRNA, consequently removing exons 14 and 15. The results of this study are consistent with the proposal that either haploinsufficiency for wild-type JAG1 and/or dominant negative effects produced by mutated JAG1 are responsible for the AGS phenotype.

Analysis of cardiovascular phenotype and genotype-phenotype correlation in individuals with a JAG1 mutation and/or Alagille syndrome.

Cardiovascular anomalies are among the most common features of Alagille syndrome (AGS). Mutations of JAG1 are found in most individuals with AGS. This study was undertaken to determine the spectrum of cardiovascular phenotypes associated with a JAG1 mutation and/or AGS, investigate potential genotype-phenotype correlations, and begin to correlate clinical outcome with genetic pathogenesis. We reviewed the records of 200 individuals with a JAG1 mutation or AGS. A total of 187 (94%) subjects had evidence of cardiovascular involvement. Cardiovascular anomalies were identified by imaging in 150 subjects (75%), and 37 (19%) had a peripheral pulmonary stenosis murmur with either a normal echocardiogram or no imaging study. Of the 150 subjects with anomalies confirmed by imaging, right-sided anomalies were present in 123 and left-sided anomalies in 22, with both in 12. Seventeen subjects had other anomalies. The most common abnormality was stenosis/hypoplasia of the branch pulmonary arteries (PAs), which was documented by imaging (n=111) or inferred from a peripheral pulmonary stenosis murmur (n=41) in 76% of subjects. Tetralogy of Fallot was present in 23 subjects and was accompanied by pulmonary atresia in 8. Branch PA phenotype differed between individuals with and without a JAG1 mutation. Among subjects with a JAG1 mutation, there was no correlation between the type or location of mutation and the frequency or type of cardiovascular anomaly. More than 90% of individuals with a JAG1 mutation or AGS have cardiovascular anomalies, with branch PA stenosis the most common abnormality. Cardiovascular phenotype does not correlate with the type or location of JAG1 mutation.

The significance of human jagged 1 mutations detected in severe cases of extrahepatic biliary atresia

Mutations of human jagged 1 (JAG1) gene are responsible for Alagille Syndrome (AGS), whose 2 main symptoms are intrahepatic bile duct hypoplasia and pulmonary stenosis. We examined the JAG1 mutation in extrahepatic biliary atresia (EHBA), which is similar in phenotype to AGS, although a different pathogenesis is suggested. In 102 cases of EHBA, 9 missense mutations were detected, including 2 intrafamilial expressions in the propositus and an aunt of one family. These mutations were all missense and sporadic except for those of this particular family. The JAG1 gene mutations were generally found in severely ill patients subjected to liver transplantation at less than 5 years of age. None of the 9 cases of EHBA revealed any of the 5 major symptoms of AGS nor any identical pathological findings after 3 years of follow-up. Our cases were clearly separated from AGS by pathological findings and clinical features, and could be diagnosed as EHBA and not as atypical AGS. The increase of interleukin 8 (IL-8) production induced by tumor necrosis factor α (TNF-α) in Huh 7 cells was suppressed by the coexistence of JAG1 protein. We examined the different influences between wild-type cells and the 3 kinds of mutants detected in EHBA on Huh 7 cells and found that 2 of 3 mutants showed about half of the repressed activity compared with that of wild type. In conclusion, these results suggest that the JAG1 gene abnormality may be an aggravating factor in EHBA. (H EPATOLOGY 2002;36:904-912.)

Tetralogy of Fallot and Other Congenital Heart Defects in Hey2 Mutant Mice

Congenital malformations of the heart and circulatory system are the most common type of human birth defect. Recent studies have implicated the Notch signaling pathway in human cardiac development by demonstrating abnormalities of the JAG1 gene as the basis for Alagille syndrome and some cases of isolated tetralogy of Fallot or pulmonic stenosis [1–4]. How the Notch pathway acts in cardiac development remains unknown, but the Hey family of basic helix-loop-helix (bHLH) transcription factors are candidates for mediating Notch signaling in the developing cardiovascular system [5–15]. Here, we use gene targeting to determine the developmental functions of mouse Hey2, a Hey family member that is expressed during the embryonic development of the heart, arteries, and other organs. Homozygotes for the Hey2 mutant allele display a spectrum of cardiac malformations including ventricular septal defects, tetralogy of Fallot, and tricuspid atresia, defects that resemble those associated with mutations of human JAG1. These results establish Hey2 as an important regulator of cardiac morphogenesis and suggest a role for Hey2 in mediating or modulating Notch signaling in the developing heart.

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.

Characterization of Notch receptor expression in the developing mammalian heart and liver.

Alagille syndrome (AGS) is an autosomal dominant disorder characterized by bile duct paucity along with cardiovascular, skeletal, and ophthalmologic defects. The identification of JAG1 as the AGS disease gene revealed the crucial role of the Notch signaling pathway in the development of multiple organ systems in humans. Patients with identical mutations in JAG1 demonstrate extreme clinical variability, suggesting that other factors may influence the severity of the developmental defects in this disorder. We have defined the temporal and spatial expression patterns of the Notch receptor genes in the developing mammalian heart and liver in order to identify potential ligand/receptor interactions during embryogenesis. In the developing heart, both Notch1 and Notch2 are expressed in the outflow tracts and the epicardium, in specific cell populations previously shown to express JAG1. These cells are destined to undergo epithelial-to-mesenchymal transformation. In the newborn mouse liver, Notch2 and Notch3 are expressed in opposing cell populations, suggesting they play different roles in cell fate determination during bile duct development. JAG1 is also expressed in cells adjacent to those expressing Notch2, suggesting a possible ligand receptor relationship. The Notch receptors have distinct roles in cell fate determination in different organ systems.

Extrahepatic biliary atresia: A disease or a phenotype?

Extrahepatic biliary atresia: A disease or a phenotype?

A mouse model of Alagille syndrome: Notch2 as a genetic modifier of Jag1 haploinsufficiency.

Alagille syndrome is a human autosomal dominant developmental disorder characterized by liver, heart, eye, skeletal, craniofacial and kidney abnormalities. Alagille syndrome is caused by mutations in the Jagged 1 (JAG1) gene, which encodes a ligand for Notch family receptors. The majority of JAG1 mutations seen in Alagille syndrome patients are null alleles, suggesting JAG1 haploinsufficiency as a primary cause of this disorder. Mice homozygous for a Jag1 null mutation die during embryogenesis and Jag1/+ heterozygous mice exhibit eye defects but do not exhibit other phenotypes characteristic of Alagille syndrome patients ( Xue, Y., Gao, X., Lindsell, C. E., Norton, C. R., Chang, B., Hicks, C., Gendron-Maguire, M., Rand, E. B., Weinmaster, G. and Gridley, T. (1999) HUM: Mol. Genet. 8, 723-730). Here we report that mice doubly heterozygous for the Jag1 null allele and a Notch2 hypomorphic allele exhibit developmental abnormalities characteristic of Alagille syndrome. Double heterozygous mice exhibit jaundice, growth retardation, impaired differentiation of intrahepatic bile ducts and defects in heart, eye and kidney development. The defects in bile duct epithelial cell differentiation and morphogenesis in the double heterozygous mice are similar to defects in epithelial morphogenesis of Notch pathway mutants in Drosophila, suggesting that a role for the Notch signaling pathway in regulating epithelial morphogenesis has been conserved between insects and mammals. This work also demonstrates that the Notch2 and Jag1 mutations interact to create a more representative mouse model of Alagille syndrome and provides a possible explanation of the variable phenotypic expression observed in Alagille syndrome patients.

Erratum: Parental mosaicism of JAG1 mutations in families with Alagille syndrome

Figure 6 in the above paper was printed with an incorrect legend. The figure and legend are reproduced correctly below.

Parental mosaicism of JAG1 mutations in families with Alagille syndrome.

The Alagille syndrome (AGS), a congenital disorder affecting liver, heart, skeleton and eye in association with a typical face, is an autosomal dominant disease with nearly complete penetrance and variable expression. AGS is caused by mutations in the developmentally important JAG1 gene. In our mutation screening, where 61 mutations in JAG1 were detected, we identified five cases where mosaicism is present. Our results point to a significant frequency of mosaicism for JAG1 mutations in AGS of more than 8.2%. Because mosaicism may be associated with a very mild phenotype, the appropriate diagnosis of AGS and consequently the determination of the recurrence risk can be complicated.

Mutation analysis of Jagged1 (JAG1) in Alagille syndrome patients Communicated by Ian McIntosh Online Citation: Human Mutation, Mutation in Brief #397 (2000) Online http://journals.wiley.com/1059-7794/pdf/mutation/397.pdf

Alagille syndrome (AGS) is an autosomal dominant disorder caused by mutations in Jagged1 (JAG1), a ligand in the evolutionarily conserved Notch signaling pathway. Previous studies have demonstrated that a wide spectrum of JAG1 mutations result in AGS. These include total gene deletions, protein truncating, splicing and missense mutations which are distributed across the coding region of the gene. Here we present results of JAG1 mutation screening by SSCP and FISH in 105 patients with AGS. For these studies, new primers were designed for 12 exons. Mutations were identified in 63/105 patients (60%). The spectrum of the JAG1 mutations presented here is consistent with previously reported results. Eighty three percent (52/63) of the mutations were protein truncating, 11% (7/63) were missense, 2% (1/63) were splice site, and 5% (3/63) were total gene deletions demonstrable by FISH. Six of the missense mutations are novel. As has been reported previously, there is no apparent relationship between genotype and clinical phenotype. Hum Mutat 17:151–152, 2001. © 2001 Wiley-Liss, Inc.

Defective intracellular transport and processing of JAG1 missense mutations in Alagille syndrome.

Jagged1 (JAG1) is a cell surface ligand in the Notch signaling pathway and mutations in this gene cause Alagille syndrome (AGS). JAG1 mutations have been identified in 60-70% of AGS patients studied, and these include total gene deletions ( approximately 6%), protein-truncating mutations (insertions, deletions and nonsense mutations) (82%) and missense mutations (12%). Based on the finding that total JAG1 deletions cause AGS, haploinsufficiency has been hypothesized to be a mechanism for disease causation; however, the mechanism by which missense mutations cause disease is not understood. To date, 25 unique missense mutations have been observed in AGS patients. Missense mutations are non-randomly distributed across the protein with clusters at the 5' end of the protein, in the conserved DSL domain, and two clusters within the EGF repeats. To understand the effect of the missense mutations on protein localization and function, we have studied four missense mutations (R184H, L37S, P163L and P871R). In two assays of JAG1 function, R184H and L37S are associated with loss of Notch signaling activity relative to wild-type JAG1. Neither R184H or L37S is present on the cell surface and both are abnormally glycosylated. Furthermore, these mutations lead to abnormal accumulation of the protein, possibly in the endoplasmic reticulum. Both P163L and P871R are associated with normal levels of Notch signaling activity and are present on the cell surface, consistent with these changes being polymorphisms rather than disease-causing mutations.