Precision Therapeutics for Monogenic Epilepsies: From Molecular Mechanisms to Disease Modification in Developmental and Epileptic Encephalopathies and Neurodevelopmental Disorders with Epilepsy

Background: Developmental and epileptic encephalopathies (DEEs) and neurodevelopmental disorders with epilepsy (NDD-E) are etiologically heterogeneous conditions historically treated with syndrome-based, symptomatic approaches. Advances in genomic sequencing have identified monogenic causes across more than 900 genes, creating opportunities for mechanism-informed and disease-modifying precision therapies. Methods: For this narrative review, PubMed/MEDLINE and ClinicalTrials.gov were searched through September 2026 using disorder-, gene-, mechanism-, and therapeutic-modality-specific terms to identify mechanism-informed and disease-modifying therapies for monogenic DEEs and NDD-E. Results: Pathogenic mechanisms include gain- or loss-of-function ion-channel abnormalities, altered neurotransmitter receptor/transporter function, impaired synaptic signaling, dysregulated intracellular pathways, metabolic deficiencies, protein misfolding, and transcriptional or epigenetic dysregulation. Across genes such as SCN1A, SCN2A, SCN8A, KCNQ2, KCNT1, KCNA2, CACNA1A, GABA-receptor subunits, SLC6A1, GRIN genes, SYNGAP1, STXBP1, DNM1, SHANK3, TSC1/TSC2, GNAO1, UBE3A, MECP2, and TCF4, therapeutic strategies range from repurposed and mechanism-targeted pharmacologic agents (e.g., sodium- and potassium-channel modulators, mTOR inhibitors) to antisense oligonucleotides, RNA interference, gene replacement or augmentation, transcriptional activation, and genome editing. Several programs have advanced from preclinical proof of concept into early- and late-phase human trials, with variant-specific functional classification increasingly guiding therapy selection, particularly distinguishing gain-of-function from loss-of-function disease. Conclusions: Precision therapeutics are shifting the treatment paradigm for monogenic DEEs and NDD-E from empiric seizure control toward mechanism-based targeting of dysregulated molecular pathways and gene-based disease-modifying therapies. Realizing this potential will require functional variant classification, delivery technologies capable of durable and cell-appropriate target engagement, and trial designs incorporating developmental and biomarker outcomes beyond seizure frequency alone to demonstrate genuine disease modification.