Deleted chromosome 20 from a patient with Alagille syndrome isolated in a cell hybrid through leucine transport selection: study of three candidate genes

Human hepatic organoids for the analysis of human genetic diseases

We developed an in vitro model system where induced pluripotent stem cells (iPSCs) differentiate into 3-dimensional human hepatic organoids (HOs) through stages that resemble human liver during its embryonic development. The HOs consist of hepatocytes, and cholangiocytes, which are organized into epithelia that surround the lumina of bile duct-like structures. The organoids provide a potentially new model for liver regenerative processes, and were used to characterize the effect of different JAG1 mutations that cause: (a) Alagille syndrome (ALGS), a genetic disorder where NOTCH signaling pathway mutations impair bile duct formation, which has substantial variability in its associated clinical features; and (b) Tetralogy of Fallot (TOF), which is the most common form of a complex congenital heart disease, and is associated with several different heritable disorders. Our results demonstrate how an iPSC-based organoid system can be used with genome editing technologies to characterize the pathogenetic effect of human genetic disease-causing mutations.

[Endocrinologic and metabolic complications of Alagille syndrome]

BACKGROUND

Patients with gastrointestinal and hepatobiliary disorders, either congenital or acquired early in childhood, are at high risk for various endocrine and metabolic abnormalities.

CASE REPORT

A 27-year-old woman with Alagille's syndrome presented with progressive jaundice and gait disturbances following surgery and ingestion of oral contraceptives. On physical examination, short stature, facial dysmorphism and neuromuscular symptoms such as polyneuropathy and spinocerebellar ataxia were noted. Serum concentrations of total bilirubin (54 mg/dl) and alkaline phosphatase were markedly increased, whereas serum levels of haptoglobin, zinc, vitamin D and E were decreased. Although prehepatic or intrahepatic etiologies of jaundice were more likely in this patient, posthepatic etiologies were ruled out by abdominal ultrasound and endoscopic retrograde cholangio-pancreaticography. Based on a working diagnosis of acute drug-induced cholestasis, treatment with high doses of lipid-soluble vitamins and ursodeoxycholic acid was initiated. In response to therapy, her abnormal laboratory results normalized and her neurologic symptoms markedly improved.

CONCLUSION

This clinicopathological conference of a patient with Alagille's syndrome illustrates the clinical presentation and therapy of metabolic and endocrine complications in chronic cholestasis.

Identification and cloning of the human homolog (JAG1) of the rat Jagged1 gene from the Alagille syndrome critical region at 20p12

Notch proteins are a family of closely related transmembrane receptors proven to be instrumental in cell fate decisions. Recently, Notch ligands Delta and Jagged have been identified in Drosophila and rat, respectively. We have isolated the human homolog of the rat Jagged1 gene, JAG1, from a CpG island in a YAC clone covering the Alagille syndrome critical region at chromosome 20p12 (tel-SNAP-D20S186-cen). Alagille syndrome is an autosomal dominant disorder characterized by neonatal jaundice, paucity of intrahepatic bile ducts, and abnormalities of the heart, skeleton, and eyes. The human Jagged1 (JAG1), therefore, appears to be a strong candidate gene for this disease. Here we describe the identification, full-length cDNA cloning, expression patterns, and precise physical location of this gene within the Alagille syndrome critical region.

Mutations in the human Jagged1 gene are responsible for Alagille syndrome

Alagille syndrome (AGS) is an autosomal-dominant disorder characterized by intrahepatic cholestasis and abnormalities of heart, eye and vertebrae, as well as a characteristic facial appearance. Identification of rare AGS patients with cytogenetic deletions has allowed mapping of the gene of 20p12. We have generated a cloned contig of the critical region and used fluorescent in situ hybridization on cells from patients with submicroscopic deletions to narrow the candidate region to only 250 kb. Within this region we identified JAG1, the human homologue of rat Jagged1, which encodes a ligand for the Notch receptor. Cell-cell Jagged/Notch interactions are known to be critical for determination of cell fates in early development, making this an attractive candidate gene for a developmental disorder in humans. Determining the complete exon-intron structure of JAG1 allowed detailed mutational analysis of DNA samples from non-deletion AGS patients, revealing three frame-shift mutations, two splice donor mutations and one mutation abolishing RNA expression from the altered allele. We conclude that AGS is caused by haploinsufficiency of JAG1.

Localization of Alagille syndrome to 20p11.2-p12 by linkage analysis of a three-generation family

Alagille syndrome (AGS) or arteriohepatic dysplasia is a rare but well-defined clinical entity that is usually inherited as an autosomal dominant trait. A limited number of patients carry a deletion in chromosome 20p, with 20p11.23-p12.2 as the area of minimal overlap. Recently, a family has been identified in which a balanced translocation with a breakpoint in 20p12 co-segregates with the AGS phenotype. Here, we report a three-generation family with AGS and in which the affected members have a normal karyotype. Linkage analysis was performed with markers from the 20p candidate region. A lod score of Z = 2.96 was obtained with D20S27 at no recombination. Combining D20S27 and D20S61 to a single highly informative locus resulted in a maximum lod score of Z = +3.56 at theta = 0.0. Haplotype analysis positioned AGS between D20S59 and D20S65, markers that define an interval of about 40 cM. Allelic loss was not observed for the tested markers and no abnormalities in the PAX1 candidate gene were detected. These findings demonstrate that the locus on chromosome 20p could be responsible for AGS in cytogenetically normal patients and argues for a general role of this locus in the aetiology of AGS.