Alagille syndrome mutation update: Comprehensive overview ofJAG1andNOTCH2mutation frequencies and insight into missense variant classification

Abstract

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.

Genome sequencing increases diagnostic yield in clinically diagnosed Alagille syndrome patients with previously negative test results

“…Previous studies have shown that these three testing strategies are capable of detecting up to~97% of pathogenic variants in ALGS. 5,6 Genome sequencing DNA was extracted from either whole blood or lymphoblastoid cell lines using the DNeasy Blood and Tissue Kit (Qiagen, Hilden, Germany). Short-read (2 × 150 bp) Illumina (Illumina, San Diego, CA) GS was performed at the Broad Institute Genomic Services (Boston, MA) using a PCR-free protocol at a targeted mean sequencing depth of 30×.…”

Peritoneal dialysis in an adult patient with tetralogy of Fallot diagnosed with incomplete Alagille syndrome

“…Cysteine loss within the JAG1 protein frequently results in missense mutations in ALGS patients [10], likely due to the unique type of bonds (disulfide bonds) that cysteine forms. Disulfide bridges between cysteine molecules are crucial for the stability of the tertiary and quaternary structures of proteins and hence, for their function.…”

“…In the presented case, we identified a previously unknown missense variant – c.587G > A – within exon 4 of the JAG1 gene, which results in an amino acid alteration (p.Cys196Tyr) in the DSL domain of JAG1 that is responsible for its binding to the Notch2 receptor [ 10 ]. Exon 4 is the second most frequent location of pathogenic variants within the JAG1 gene [ 11 ].…”

Recurrent Hepatocellular Carcinoma in an Adult With Alagille Syndrome Treated With Liver Resection Followed by Liver Transplantation: A Rare Case Report

“… 2 First described in 1969, AGS is estimated to affect 1:30 000–50 000 live births. 5 Its pathogenesis is related to mutations in JAG1 or NOTCH2 genes 1 that are expressed in fetal liver, lungs, brain, and kidneys, as well as adult heart, lung, skeletal muscle, and kidneys. AGS is most commonly associated with paucity of intrahepatic bile ducts that may lead to chronic cholestasis, as well as cardiac (pulmonary stenosis), ocular, and skeletal abnormalities (characteristic facial features).…”