Biomedical subjects

Kedous Y Mekbib

Publications and source records attributed to Kedous Y Mekbib.

4 recordsLinked to original sources

PubMed2026

Microglial GRB2 is essential for brain ventriculogenesis and CSF homeostasis.

Microglia play essential yet poorly understood roles in brain development, including axon guidance, regulation of neurogenesis, and pruning of neuronal projections. Congenital hydrocephalus (CH), characterized by enlarged cerebrospinal fluid (CSF)-filled ventricles, is a leading cause of pediatric brain surgery, but its molecular mechanisms remain unclear. We have identified what we believe to be novel, recurrent, damaging missense variants in the SH3-binding domain of the adaptor protein Growth Factor Receptor-Bound Protein 2 (GRB2) in unrelated patients with CH. GRB2 is significantly co-expressed with one of its known upstream receptor tyrosine kinase partners, CSF1R, in the developing human brain, particularly in a microglial subtype associated with regulation of neural stem cells. Immunoprecipitation validated GRB2-CSF1R binding in mouse microglial cells and human monocyte cell line. Cx3cr1-Grb2fl/fl mice engineered with conditional deletion of Grb2 in microglia exhibit congenital absence of microglia and early postnatal severe communicating (non-obstructive) hydrocephalus, mimicking GRB2-mutant patients. The severe ventriculomegaly of Cx3cr1-Grb2fl/fl mice is associated with both depletion of cerebral cortical neurons and impairment of glia-lymphatic-mediated CSF flow. Together, these findings implicate a role of GRB2 in microglia that could be essential for brain development and CSF homeostasis.

Genetics↗

PubMed2026

De novo chromatin remodelling variants in sporadic Chiari 1 malformation.

Chiari 1 malformation (CM1) is the most common congenital malformation of the human hindbrain. Although prior studies have implicated chromatin-remodeling genes in CM1, the de novo genetic architecture and underlying neurodevelopmental mechanisms remain incompletely defined. To investigate the molecular genetics of a novel familial form of CM1 linked with syringomyelia and tethered cord and determine whether rare, damaging de novo variants (DNVs) contribute to sporadic CM1 risk with gene- and pathway-level resolution, we performed whole-exome sequencing in an ultra-rare multigenerational family with CM1 and associated spinal pathology, and in the largest assembled trio-based cohort to date, comprising 1,585 proband-parent trios with sporadic, idiopathic CM1 (2017-2025). The comparison cohort included 1,798 unaffected control siblings. Clinical phenotyping was by systematic medical record review. Structural domain mapping, in silico modeling, and integration with single-cell transcriptomic data from developing human cerebellum was conducted to assess biological plausibility. A heterozygous loss-of-function variant in CHD3 segregated with CM1 and syringomyelia in a multigenerational family. In the trio-based cohort, rare protein-altering DNVs were significantly enriched across multiple chromodomain helicase DNA-binding (CHD) genes, including CHD1, CHD3, CHD4, and CHD8, exceeding gene-specific mutation expectations (protein-damaging variants: P = 1.3 × 10-9; predicted loss-of-function variants: P = 8.6 × 10-5). CHD1 contained two pathogenic DNVs (p.A999D and p.E984K). CHD4 (p.D744N, p.T1813P, and p.I1102T) and CHD8 (p.R1402X, p.R1472X, and p.R2035X) each contained three new DNVs. Variants clustered within conserved ATPase, helicase, and chromodomain regions essential for chromatin remodeling, and these patients frequently had comorbid developmental delay and related neurodevelopmental features. Single-cell transcriptomic analyses demonstrated enrichment in Purkinje cells and inhibitory neurons of midgestational cerebellum, where CHD gene products form a coherent chromatin-regulatory network. Rare, large-effect DNVs that disrupt chromatin-remodeling programs contribute to sporadic CM1, implicating genetically encoded dysregulation of cerebellar development as a central disease mechanism. Exome sequencing may complement surgical evaluation of children with sporadic CM1, particularly when accompanied by neurodevelopmental concerns, informing prognosis and family counseling.

de novo variants↗

PubMed2026

Developmental genetic determinants of the human cerebrospinal fluid-ventricular system.

Primary enlargement of the cerebrospinal fluid (CSF)-filled brain ventricles, known as congenital cerebral ventriculomegaly (CCV), is a hallmark of congenital hydrocephalus. CCV is also enigmatically but frequently associated with autism and other neurodevelopmental disorders. To gain insight into the developmental genetic regulation of the human CSF-ventricular system, we conducted an integrated, multiomic study of about 2700 trio-based exomes from patients with primary CCV. We found that about 25% of cases were associated with rare, damaging de novo variants in mutation-intolerant genes, many of which are linked to other dominant Mendelian disorders. Thirty-five exome-wide significant CCV genes and dozens of other high-confidence CCV genes converged on pathways involved in ATP-dependent Brahma-related gene 1/Brahma-associated factor chromatin remodeling, histone H3 lysine 4 methylation, and phosphoinositide 3-kinase signaling. Knockout of selected CCV genes in mouse models supported that de novo variants in CCV genes caused ventriculomegaly by impairing both CSF dynamics and cortical cytoarchitecture through dysregulation of neuroprogenitor cell growth and maturation in the ventricular and subventricular zones. These findings indicated that genetic and epigenetic programs coordinate the "hand-in-glove" development of the CSF-ventricular system with that of the cerebral cortex and establish a genetic connection between CCV and neurodevelopmental disorders, potentially explaining why some patients with hydrocephalus continue to exhibit CCV and neurodevelopmental disorders despite CSF shunting. We suggest that combined brain imaging and whole-exome sequencing could enable early detection of, and intervention for, autism and other neurodevelopmental disorders.

Humans↗

PubMed2026

De Novo TRIO Missense Variants Disrupt Ras-GEF Domains and Cause Congenital Ventriculomegaly and Hydrocephalus.

Congenital hydrocephalus (CH), characterized by congenital ventriculomegaly (CV), affects approximately 0.5-1 per 1000 live births and is a common cause of pediatric neurosurgical intervention, yet its genetic architecture remains incompletely defined. We report a child with syndromic CH requiring cerebrospinal fluid diversion who harbored a pathogenic de novo missense variant in TRIO (c.3232C > T; p.(Arg1078Trp)), a gene previously associated with autosomal dominant neurodevelopmental disorders featuring variable head circumference. This case prompted systematic evaluation of TRIO variation in our CV/CH cohort (2,697 patient-parent trios) using exome sequencing. We identified five additional unrelated probands with de novo TRIO variants, including two novel substitutions affecting the same residue within the Ras-GEF1 domain (p.(Glu1299Lys) and p.(Glu1299Gly)), yielding significant gene-level enrichment for protein-damaging de novo variants (adjusted p = 6.12 × 10-5). All affected individuals exhibited CV, frequently accompanied by developmental delay and additional structural brain abnormalities. In silico structural modeling predicted that associated variants destabilize critical TRIO Ras-GEF domains required for Rho GTPase activation. Analysis of single-nucleus transcriptomic data from the developing human neocortex revealed enrichment of TRIO expression in multipotent progenitor populations. A systematic literature review identified six additional individuals with TRIO de novo variants and reported CV or CH, including an unrelated patient with the same p.(Arg1078Trp) substitution. Together, these findings expand the phenotypic spectrum associated with pathogenic TRIO variation to include CV/CH and support TRIO as a clinically relevant gene in the genetic evaluation of syndromic CV/CH patients.

Humans↗