A New Model of Alagille Syndrome With Broad Phenotypic Representation

Notch signaling pathway: architecture, disease, and therapeutics

The NOTCH gene was identified approximately 110 years ago. Classical studies have revealed that NOTCH signaling is an evolutionarily conserved pathway. NOTCH receptors undergo three cleavages and translocate into the nucleus to regulate the transcription of target genes. NOTCH signaling deeply participates in the development and homeostasis of multiple tissues and organs, the aberration of which results in cancerous and noncancerous diseases. However, recent studies indicate that the outcomes of NOTCH signaling are changeable and highly dependent on context. In terms of cancers, NOTCH signaling can both promote and inhibit tumor development in various types of cancer. The overall performance of NOTCH-targeted therapies in clinical trials has failed to meet expectations. Additionally, NOTCH mutation has been proposed as a predictive biomarker for immune checkpoint blockade therapy in many cancers. Collectively, the NOTCH pathway needs to be integrally assessed with new perspectives to inspire discoveries and applications. In this review, we focus on both classical and the latest findings related to NOTCH signaling to illustrate the history, architecture, regulatory mechanisms, contributions to physiological development, related diseases, and therapeutic applications of the NOTCH pathway. The contributions of NOTCH signaling to the tumor immune microenvironment and cancer immunotherapy are also highlighted. We hope this review will help not only beginners but also experts to systematically and thoroughly understand the NOTCH signaling pathway.

Occipitocervical Osteotomies and Interfacet Grafts for Reduction of Occipitocervical Kyphosis and Basilar Invagination

BACKGROUND

Occipitocervical congenital pathologies involving instability of the atlantoaxial joint and basilar invagination are challenging to treat owing to the complex anatomy involving neurovascular structures at the skull base and the high-risk nature of surgery close to the brainstem.

CASE DESCRIPTION

A patient presented with Alagille syndrome with multiple segmentation/fusion anomalies of the cervical spine and craniocervical junction, including fusion of the skull base and occipital condyles and partial assimilation of the C1 anterior ring and C2 dens. The head was anteriorly displaced, with C2 located immediately below the foramen magnum. There was significant kyphotic angulation due to nonunion of the base of the dens and the body of C2. The patient underwent occipitocervical osteotomies and occiput-C2 interfacet grafts for reduction of occipitocervical kyphosis along with foramen magnum decompression and occiput-C6 fusion. The patient had significant neurologic improvement and sustained improved craniocervical alignment on last follow-up.

CONCLUSIONS

In patients with atlantoaxial instability with basilar invagination, posterior facet release, local distraction, and placement of cortical bone interbody grafts with occipitocervical fusion may be instrumental in reducing craniocervical kyphosis and compression by allowing anterior translation of the upper cervical spine relative to the skull. This method may be a safe and effective posterior-only approach for brainstem/spinal cord decompression for patients with complex craniocervical congenital malformations.

Alagille Syndrome: A Novel Mutation in JAG1 Gene

Alagille syndrome is an autosomal dominant multisystem disorder with variable phenotypic penetrance, caused by heterozygous mutations in JAG1 or NOTCH2, encoding for the components of the Notch signaling pathway. In this paper, we described a novel mutation not yet reported in literature. This 3-years old male child was referred to our Clinical Genetics Unit because of delayed psychomotor development, systolic murmur, dysmorphic facial features, and hypertransaminasemia. The novel JAG1 heterozygous c.2026delT variant in exon 16 was found. JAG1 mutations are classified as protein truncating and non-protein truncating, without any genotype-phenotype correlation. The detected mutation determines a stop codon (p.Cys676AlafsTer67) in the gene sequence, encoding a truncated protein. Our report broadens the spectrum of JAG1 gene mutations.

A Novel c.91dupG JAG1 Gene Mutation Is Associated with Early Onset and Severe Alagille Syndrome

Alagille syndrome (MIM 118450) is an autosomal dominant disorder characterized by paucity of intrahepatic bile ducts, chronic cholestasis, pulmonary stenosis, butterfly-like vertebrae, posterior embryotoxon, and dysmorphic facial features. Most cases are caused by JAG1 gene mutations. We report the case of a 2-year-old Mexican mestizo patient with Alagille syndrome, having exhibited jaundice and cholestatic syndrome as of three weeks of age. Sequencing analysis of the JAG1 gene revealed the novel heterozygous mutation c.91dupG that originates a truncated protein and therefore a possibly diminished activation of the Notch signaling pathway. The latter may explain the severe phenotype of the patient. Since the mutation was not identified in the parents, it was considered a de novo event, highlighting the importance of molecular diagnosis and genetic counseling. In conclusion, this report widens the spectrum of JAG1 gene mutations associated with Alagille syndrome.