Characterization of CTNND2-related neurodevelopmental disease, phenotype-genotype spectrum and WNT dynamics in early neurogenesis.

Background: Heterozygous variants in CTNND2, encoding the brain-specific protein δ-catenin, are associated with a broad spectrum of neurodevelopmental disorders, including dyslexia, attention deficit hyperactivity disorder, intellectual disability, and autism. Despite its clinical significance, the full phenotypic spectrum of CTNND2-associated disorders and the neurodevelopmental role of δ-catenin, a key component of the cadherin-catenin cell adhesion complex, remain poorly defined. Methods: Through international collaboration, we assembled the phenotypic and molecular information for 57 individuals, 42 previously unpublished, carrying heterozygous CTNND2 variants. All individuals were evaluated by local clinicians, and the variants were identified through exome or genome sequencing, clinical microarray, or karyotyping. To investigate the effects of δ-catenin loss on early neurogenesis, we performed neural differentiation and transcriptomic profiling in three patient-derived neural stem cell lines and three CRISPR-Cas9-generated CTNND2 knockout lines. In one patient-derived line, we further analyzed cerebral organoid development and performed pathway modulation to assess phenotypic rescue. Results: The 41 CTNND2 variants included 12 previously reported loss-of-function- and one missense variant, and 28 novel variants comprising 10 missense and 18 predicted loss-of-function changes. Eight of the novel variants occurred de novo, and 12 were inherited from a parent with a neurodevelopmental phenotype. The most common clinical features were developmental delay (90%), intellectual disability (74%), and behavioral abnormalities (79%). Functional studies revealed impaired early neurogenesis in one patient-derived line, characterized by aberrant neural rosette formation. Transcriptome analysis showed dysregulated WNT signaling, and partial rescue of these defects was achieved by modulating the WNT pathway, highlighting δ-catenin's role in early neural development. Conclusions: This study defines the clinical symptoms of CTNND2-related neurodevelopmental disorders, outlining a recognizable yet variable phenotype that overlaps with other forms of intellectual disability and autism. Our findings provide preliminary evidence of genotype-phenotype correlations and highlight δ-catenin's critical role in modulating WNT signaling during early neural development. These insights advance our understanding of CTNND2-associated disorders and support the importance of mechanistic studies to inform personalized diagnostics and therapies.