Novel Heterozygous Mutations in JAG1 and NOTCH2 Genes in a Neonatal Patient with Alagille Syndrome

Alagille Syndrome: Unraveling the Complexities of Genotype-Phenotype Relationships and Exploring Avenues for Improved Diagnosis and Treatment

Alagille syndrome (ALGS) is a rare genetic disorder caused by mutations in the JAG1 and NOTCH2 genes, leading to a wide range of clinical manifestations. This review explores the complex genetic and clinical landscape of ALGS, emphasizing the challenges in understanding genotype-phenotype relationships due to its rarity and the lack of suitable research models. The review projects a clinical overview of the disease, emphasizing the influence of potential gene modifiers on its clinical presentation and the lack of mechanistic studies for over 100 mutations identified in the last 24 years from various populations, representing a significant gap in our current knowledge and advocating for further exploration. The review addresses the diagnostic challenges posed by the variable expressivity and overlapping symptoms of ALGS. It summarizes current treatment options and discusses emerging approaches such as antisense oligonucleotides (ASOs) and gene therapies. Further, the need for improved diagnostic tools, a deeper understanding of the underlying mechanisms, and the development of targeted therapies are emphasized using zebrafish and mice models, as well as genome editing for variant analysis and stem cell organoid models for disease modeling and drug discovery. The importance of cohort-based studies in understanding the natural history and outcomes of ALGS in diverse populations is highlighted. The review concludes by emphasizing the need for multi-disciplinary collaborative research to address the challenges in ALGS diagnosis, prognosis, and treatment, particularly for underrepresented populations.

Broadening the clinical spectrum of ALGS: an Egyptian cohort with five novel mutations in JAG1 gene

Background

Alagille syndrome (ALGS) is a rare autosomal dominant multisystem disorder that affects the liver, heart, eyes, vertebrae, and kidneys and is associated with characteristic facies. This work aimed to study the spectrum of the clinical features of ALGS in an Egyptian cohort of patients in conjunction with partial sequencing of the JAG1 gene.

Methods

This study included 17 pediatric ALGS patients diagnosed on clinical grounds: facial features, cholestatic liver disease, and cardiac, vertebral, and ocular findings. Molecular analysis was conducted in 10 selected exons of the JAG1 gene.

Results

The clinical features of ALGS included cholestatic liver disease (100%), facial dysmorphism (100%), cardiac abnormalities (88.2%), butterfly vertebrae (64.7%), posterior embryotoxon (35.2%), poor growth (41%), xanthomata (11.8%), and hiatus hernia (11.8%). Five novel pathogenic JAG1 mutations were identified in this study, including two nonsense mutations, one splicing mutation, one frameshift insertion, and one frameshift deletion. In two patients, the mutations were confirmed to be de novo, as the mutations could not be detected in both parents.

Conclusion

Five novel JAG1 pathogenic variants were identified in this study. This is the first molecular study to report pathogenic mutations in the JAG1 gene within an Egyptian cohort of children with ALGS.

Biological Significance of NOTCH Signaling Strength

The evolutionarily conserved NOTCH signaling displays pleotropic functions in almost every organ system with a simple signaling axis. Different from many other signaling pathways that can be amplified via kinase cascades, NOTCH signaling does not contain any intermediate to amplify signal. Thus, NOTCH signaling can be activated at distinct signaling strength levels, disruption of which leads to various developmental disorders. Here, we reviewed mechanisms establishing different NOTCH signaling strengths, developmental processes sensitive to NOTCH signaling strength perturbation, and transcriptional regulations influenced by NOTCH signaling strength changes. We hope this could add a new layer of diversity to explain the pleotropic functions of NOTCH signaling pathway.

Midkine's Role in Cardiac Pathology

Midkine (MDK) is a heparin-binding growth factor that is normally expressed in mid-gestational development mediating mesenchymal and epithelial interactions. As organisms age, expression of MDK diminishes; however, in adults, MDK expression is associated with acute and chronic pathologic conditions such as myocardial infarction and heart failure (HF). The role of MDK is not clear in cardiovascular disease and currently there is no consensus if it plays a beneficial or detrimental role in HF. The lack of clarity in the literature is exacerbated by differing roles that circulating and myocardial MDK play in signaling pathways in cardiomyocytes (some of which have yet to be elucidated). Of particular interest, serum MDK is elevated in adults with chronic heart failure and higher circulating MDK is associated with worse cardiac function. In addition, pediatric HF patients have higher levels of myocardial MDK. This review focuses on what is known about the effect of exogenous versus myocardial MDK in various cardiac disease models in an effort to better clarify the role of midkine in HF.