De novo pathogenic variants in neuronal differentiation factor 2 (NEUROD2) cause a form of early infantile epileptic encephalopathy
- J Med Genet. 2019 Feb;56(2):113-122. doi: 10.1136/jmedgenet-2018-105322.
- 1. Pediatric Genomics Discovery Program, Department of Pediatrics, Yale University School of Medicine, New Haven, Connecticut, USA.
- 2. Division of Genetics and Metabolism, Phoenix Children's Hospital, Phoenix, Arizona, USA.
- 3. Genetics and Genome Biology Program, Research Institute, The Hospital for Sick Children, Toronto, Ontario, Canada.
- 4. Division of Clinical and Metabolic Genetics, Department of Pediatrics, University of Toronto, Toronto, Ontario, Canada.
- 5. Institute of Medical Sciences, University of Toronto, Toronto, Ontario, Canada.
- 6. GeneDx, Gaithersburg, Maryland, USA.
- 7. Department of Genetics, Yale University School of Medicine, New Haven, Connecticut, USA.
- # Contributed equally.
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.