Background: Early infantile epileptic encephalopathies are severe disorders consisting of early-onset refractory seizures accompanied often by significant developmental delay. The increasing availability of next-generation sequencing has facilitated the recognition of single gene mutations as an underlying aetiology of some forms of early infantile epileptic encephalopathies.
Objectives: This study was designed to identify candidate genes as a potential cause of early infantile epileptic encephalopathy, and then to provide genetic and functional evidence supporting patient variants as causative.
Methods: We used whole exome sequencing to identify candidate genes. To model the disease and assess the functional effects of patient variants on candidate protein function, we used in vivo CRISPR/Cas9-mediated genome editing and protein overexpression in frog tadpoles.
Results: We identified novel de novo variants in neuronal differentiation factor 2 (NEUROD2) in two unrelated children with early infantile epileptic encephalopathy. Depleting neurod2 with CRISPR/Cas9-mediated genome editing induced spontaneous seizures in tadpoles, mimicking the patients' condition. Overexpression of wild-type NEUROD2 induced ectopic neurons in tadpoles; however, patient variants were markedly less effective, suggesting that both variants are dysfunctional and likely pathogenic.
Conclusion: This study provides clinical and functional support for NEUROD2 variants as a cause of early infantile epileptic encephalopathy, the first evidence of human disease caused by NEUROD2 variants.
Keywords: epilepsy and seizures; epileptic encephalopathy; neurod2; neuronal differentiation factor; xenopus.
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