Neurodevelopmental disorder with microcephaly and seizures Cell Models for Research

Neurodevelopmental disorder with microcephaly and seizures (NDMS) is a rare genetic condition characterized by intellectual disability, microcephaly, and early-onset seizures. The exact prevalence is unknown, but it is considered ultra-rare. According to the World Health Organization (WHO), neurodevelopmental disorders affect millions worldwide, with significant impact on quality of life. The clinical burden includes lifelong cognitive impairment, motor deficits, and epilepsy, requiring multidisciplinary care. The 5-year survival is generally high, but comorbidities can reduce life expectancy. Early diagnosis and intervention are critical for improving outcomes.

NDMS is an ideal model for studying neurodevelopment and synaptic function. The disorder encompasses multiple genetic subtypes, each with distinct molecular mechanisms. Public datasets, such as those in ClinVar and DECIPHER, provide genotype-phenotype correlations. Open questions include the precise role of specific genes in cortical development and epileptogenesis. Gene-edited cell models enable functional validation of variants and mechanistic studies, bridging the gap between genetic findings and therapeutic development.

The pathogenesis of NDMS involves several key pathways:

• • Cortical Development: Genes such as WDR62, ASXL3, and CDK5RAP2 are involved in neurogenesis, neuronal migration, and cortical lamination. Disruption leads to microcephaly.
• • Synaptic Transmission: Mutations in genes encoding synaptic proteins (e.g., STXBP1, SNAP25) impair neurotransmitter release, contributing to seizures.
• • DNA Damage Response: Some genes (e.g., ATR, ATRX) are involved in DNA repair; defects cause genomic instability and apoptosis in neural progenitors.
• • mTOR Signaling: Dysregulation of the mTOR pathway (e.g., TSC1, TSC2) leads to abnormal cell growth and cortical malformations, associated with epilepsy.

Data from ClinVar and DECIPHER.

Key signaling networks implicated in NDMS:

• • Wnt/β-catenin: Regulates neural progenitor proliferation. Mutations in WNT genes or downstream components disrupt cortical development.
• • MAPK/ERK: Involved in cell proliferation and differentiation. Aberrant activation can lead to abnormal brain size.
• • PI3K/AKT/mTOR: Critical for cell growth and survival. Hyperactivation causes cortical malformations and seizures.
• • Notch: Influences neural stem cell maintenance. Altered signaling affects neurogenesis.
• • Synaptic Vesicle Cycling: Proteins like STXBP1 and SNAP25 are essential for neurotransmitter release; mutations impair synaptic transmission.

Organoids, such as cerebral organoids, recapitulate early brain development and are valuable for studying microcephaly. They can be generated from patient iPSCs and gene-edited to introduce or correct mutations.

Animal models for NDMS include:

• • Genetically Engineered Mouse Models (GEMMs): Knockout or knock-in mice for genes like Wdr62, Asxl3, and Cdk5rap2 exhibit microcephaly and seizures.
• • Patient-Derived Xenografts (PDX): Not commonly used for neurodevelopmental disorders, but brain organoids can be transplanted into mice for in vivo studies.
• • Induced Models: Chemical or viral-induced models to mimic specific aspects, such as seizures via kainic acid.

CRISPR-based gene editing enables the creation of isogenic cell lines with precise mutations. For NDMS, researchers can generate:

• • Knockout lines: For tumor suppressor genes or genes involved in neurodevelopment, such as WDR62 knockout in SH-SY5Y cells.
• • Knock-in lines: Introducing patient-specific point mutations, e.g., ASXL3 R693* in iPSC-derived neurons.
• • Reporter lines: Tagging genes with fluorescent markers to study expression and localization.

These models are sequence-verified and commercially available from various sources, accelerating research without the need for in-house editing. They are essential for functional validation and drug screening.

Gene-edited cell lines allow functional validation of disease-associated variants. For example, WDR62 knockout in neural progenitors leads to reduced proliferation and premature differentiation, confirming its role in microcephaly. Similarly, STXBP1 knockout in neurons impairs synaptic transmission, linking the gene to epilepsy. These models help prioritize candidate genes from sequencing studies.

Isogenic pairs (wild-type vs. mutant) are powerful for drug screening. For NDMS, screens can identify compounds that rescue the phenotype, such as molecules that enhance neurogenesis or reduce seizure activity. For example, a CDK5RAP2 mutant line can be used to test drugs that stabilize centrosomes. Additionally, resistance models can be developed to study why certain seizures become refractory to treatment.

CRISPR screens can identify synthetic lethal interactions or biomarkers. For instance, a genome-wide knockout screen in WDR62-deficient cells may reveal genes whose loss exacerbates or rescues the phenotype. Such screens can uncover novel therapeutic targets and biomarkers for early diagnosis.