Paucity of Interlobular Bile Ducts in Multidrug-Resistant P-Glycoprotein 3 (MDR3) Deficiency.

Multidrug-resistant P-glycoprotein 3 (MDR3) is a phospholipid translocator encoded by the ABCB4 gene located on chromosome 7. MDR3 mediates the translocation of phosphatidylcholine across the canalicular membrane of the hepatocyte into bile. Severe MDR3 deficiency typically occurs during childhood with progressive cholestasis evolving to cirrhosis and liver failure, requiring liver transplantation. In this article, we report 2 pediatric cases of severe MDR3 deficiency with paucity of interlobular bile ducts. Both underwent living donor liver transplantation at our center for decompensated liver disease and portal hypertension. We diagnosed severe MDR3 deficiency in both the cases with negative MDR3 immunostaining in the explanted liver. Genetic studies revealed homozygous deletion single base pair deletion in exon 24 of the ABCB4 gene in the second child. The patients are on regular follow-up after liver transplant and are doing well. Our report highlights that cholangiopathy in MDR3 deficiency can lead to ductopenia in pediatric livers.

Discordant clinical phenotype in monozygotic twins with Alagille syndrome: Possible influence of non-genetic factors.

Alagille syndrome is a multisystem developmental disorder characterized by bile duct paucity, congenital heart disease, vertebral anomalies, posterior embryotoxon, and characteristic facial features. Alagille syndrome is typically the result of germline mutations in JAG1 or NOTCH2 and is one of several human diseases caused by Notch signaling abnormalities. A wide phenotypic spectrum has been well documented in Alagille syndrome. Therefore, monozygotic twins with Alagille syndrome provide a unique opportunity to evaluate potential phenotypic modifiers such as environmental factors or stochastic effects of gene expression. In this report, we describe an Alagille syndrome monozygotic twin pair with discordant placental and clinical findings. We propose that environmental factors such as prenatal hypoxia may have played a role in determining the phenotypic severity.

Low incidence of alpha-1-antitrypsin deficiency in Iranian patients with neonatal cholestasis.

BACKGROUND/AIMS: There is little data concerning the incidence of alpha-1-antitrypsin"(AAT) deficiency, the most common genetic cause of liver disease, among children with neonatal cholestasis in Iran. Thus, this study was performed to analyze AAT deficiency in this group of patients. MATERIALS AND METHODS: DNA samples from patients with neonatal cholestasis were investigated for Pi S and Pi Z alleles, using polymerase chain reaction-restriction fragment length polymorphism. RESULTS: Thirty patients with neonatal cholestasis were enrolled. Among those who underwent biopsies, the results revealed neonatal hepatitis in 19, bile duct paucity in 1, steatohepatitis in 1, bile duct proliferation in 1, cirrhosis in 2, fibrosis in 2, and extrahepatic biliary atresia in 1 patient. No mutant allele was found in any patient. CONCLUSION: The incidence of AAT deficiency is very low in Iran; therefore, screening for AAT is not recommended for patients with neonatal cholestasis in Iran.

[Advances in the diagnosis and treatment of Alagille syndrome].

Alagille syndrome (ALGS), also known as arteriohepatic dysplasia, is an autosomal dominant disease with multisystem involvement. In this disease, the Notch signalling pathway is impaired due to mutation in JAG1 (ALGS type 1) or NOTCH2 (ALGS type 2) gene, affecting multiple organs or systems such as liver, heart, eyes, vertebrate and face. The main clinical features of ALGS include chronic cholestasis, congenital heart disease, mild vertebral segmentation abnormalities, characteristic face, postcorneal embryotoxon and poor kidney development. This article reviews the recent advances in the pathogenesis, clinical presentations, diagnosis and treatment of this syndrome.

Atypical causes of cholestasis.

Cholestatic liver disease consists of a variety of disorders. Primary sclerosing cholangitis and primary biliary cirrhosis are the most commonly recognized cholestatic liver disease in the adult population, while biliary atresia and Alagille syndrome are commonly recognized in the pediatric population. In infants, the causes are usually congenital or inherited. Even though jaundice is a hallmark of cholestasis, it is not always seen in adult patients with chronic liver disease. Patients can have "silent" progressive cholestatic liver disease for years prior to development of symptoms such as jaundice and pruritus. In this review, we will discuss some of the atypical causes of cholestatic liver disease such as benign recurrent intrahepatic cholestasis, progressive familial intrahepatic cholestasis, Alagille Syndrome, biliary atresia, total parenteral nutrition induced cholestasis and cholestasis secondary to drug induced liver injury.

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.

The vertebrate segmentation clock and its role in skeletal birth defects.

The segmental structure of the vertebrate body plan is most evident in the axial skeleton. The regulated generation of somites, a process called somitogenesis, underlies the vertebrate body plan and is crucial for proper skeletal development. A genetic clock regulates this process, controlling the timing of somite development. Molecular evidence for the existence of the segmentation clock was first described in the expression of Notch signaling pathway members, several of which are expressed in a cyclic fashion in the presomitic mesoderm (PSM). The Wnt and fibroblast growth factor (FGF) pathways have also recently been linked to the segmentation clock, suggesting that a complex, interconnected network of three signaling pathways regulates the timing of somitogenesis. Mutations in genes that have been linked to the clock frequently cause abnormal segmentation in model organisms. Additionally, at least two human disorders, spondylocostal dysostosis (SCDO) and Alagille syndrome (AGS), are caused by mutations in Notch pathway genes and exhibit vertebral column defects, suggesting that mutations that disrupt segmentation clock function in humans can cause congenital skeletal defects. Thus, it is clear that the correct, cyclic function of the Notch pathway within the vertebrate segmentation clock is essential for proper somitogenesis. In the future, with a large number of additional cyclic genes recently identified, the complex interactions between the various signaling pathways making up the segmentation clock will be elucidated and refined.

Notch signaling in development and disease.

Notch receptors and ligands were first identified in flies and worms, where they were shown to regulate cell proliferation, cell differentiation, and, in particular, binary cell fate decisions in a variety of developmental contexts. The first mammalian Notch homolog was discovered to be a partner in a chromosomal translocation in a subset of human T-cell leukemias. Subsequent studies in mice and humans have shown that Notch signaling plays essential roles at multiple stages of hematopoiesis, and also regulates the development or homeostasis of cells in many tissues and organs. Thus, it is not surprising that mutations which disrupt Notch signaling cause a wide range of cancers and developmental disorders. Perhaps because it is so widely used, Notch signaling is subject to many unusual forms of regulation. In this review, we will first outline key aspects of Notch signaling and its regulation by endocytosis, glycosylation, and ubiquitination. We will then overview recent literature elucidating how Notch regulates cell-lineage decisions in a variety of developmental contexts. Finally, we will describe the roles of dysregulated Notch signaling in causing several types of cancer and other pathologies.

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.

Alagille syndrome with interstitial 20p deletion derived from maternal ins(7;20).

We present a 6-year-old Chinese boy with Alagille syndrome and an interstitial 20p deletion, with a karyotype of 46,XY,der(20)dir ins(7;20)(q11.23;p11.23p12.2 or p12.2p13)mat. He had a peculiar face and suffered from congenital heart disease, growth retardation, severe cholestasis, hepatosplenomegaly, and impaired renal function. The karyotype of his mother showed a balanced translocation, 46,XX,dir ins(7;20)(q11.23; p11.23p12.2 or p12.2p13), and her phenotype was normal. His dead elder brother was highly suspected as another victim of Alagille syndrome. The findings in the present family suggested that if Alagille syndrome is a single gene defect, the putative gene responsible for the syndrome would not be located at the insertion breakpoints but located within the deletion extent.

Alagille syndrome: family studies.

Alagille syndrome (AGS) is one of the major forms of chronic liver disease in childhood with severe morbidity and a mortality of 10 to 20%. It is characterised by cholestasis of variable severity with paucity of interlobular bile ducts and anomalies of the cardiovascular system, skeleton, eyes, and face. Previous studies suggest a wide variation in the expression of the disease and a high incidence of new mutations. To determine more accurately the rate of new mutations and to develop criteria for detecting the disorder in parents we systematically investigated parents in 14 families with an affected child. Clinical examination was supplemented by liver function tests, echocardiography, radiographic examination of the spine and forearm, ophthalmological assessment, and chromosome analysis. Six parents had typical anomalies in two or more systems pointing to the presence of autosomal dominant inheritance. Systematic screening of parents for the features defined in this study should improve the accuracy of genetic counselling.

Paucity of interlobular bile ducts.

Paucity of interlobular bile ducts (PIBD) is defined as the reduction in the number of interlobular bile ducts. Paucity could be defined using the ratio of the number of portal tracts devoid of bile duct to the total number of portal tracts. At least 10 complete portal areas must be examined. In the past, only wedge biopsies could provide such samples, but now it can be achieved with needle biopsy. Usually, two types of PIBD, syndromatic and nonsyndromatic, are considered. In the syndromatic type, paucity is a major feature of the disease. In the nonsyndromatic type, paucity is only a part of the disease, as in peroxisomal disorders or alpha 1-antitrypsine (A1AT) deficiency, and is an inconstant finding. Opacification of the intrahepatic bile ducts in infants with nonsyndromatic paucity with no associated disorder demonstrates sclerosing cholangitis in at least half of patients in whom the diagnosis of "idiopathic paucity" would have been made a few years ago. The remaining patients must be considered as waiting for the identification of new disorders associated with paucity.