Authors :
Presenting Author: Caeley Reever, MS – University of Virginia School of Medicine
Alexis Boscia, BS – University of Virginia
Tyler Deutsch, BS – University of Virginia
Mansi Patel, BS – University of Virginia
Raquel Miralles, PhD – University of Virginia
Shrinidhi Kittur, BS – University of Virginia
Mathew Yorek, MS – University of Virginia
Manoj Patel, PhD – University of Virginia
Rationale:
De novo mutations in SCN8A, the gene that encodes the Nav1.6 sodium channel, causes developmental and epileptic encephalopathy (DEE), a severe epilepsy syndrome characterized by seizures, cognitive dysfunction, movement disorders and sudden unexpected death in epilepsy (SUDEP). Current treatments, including anti-seizure medications that broadly target sodium channels, are ineffective in SCN8A DEE patients1 thus underscoring the urgent need for more precise interventions. In this study, we used adenine base editors to correct the R1872W SCN8A-DEE causing mutation in a mouse model2, consequently targeting the underlying mechanism of the disorder.
Methods:
EMX1-Cre mice were crossed with Scn8aW/+ mice to express the R1872W variant exclusively in forebrain excitatory neurons (Scn8aW/+-EMX1)2. The adenine base editor and guide RNA (SCN8A-ABE) was packaged within PhP.eB-adeno-associated viruses (AAVs). Mice were injected intracerebroventricularly with SCN8A-ABE and PhP.eB-GFP (ABE Treated). Control littermates were injected with PhP.eB-GFP (Sham Untreated). Seizures were monitored using 24hr video and electroencephalogram (EEG) recordings. Electrophysiological recordings were conducted on Scn8aW/+-EMX1 mice at the time point corresponding to seizure onset in EEGs.
Results:
SCN8A-ABE treatment significantly prolonged the survival of approximately 90% of Scn8aW/+-EMX1 ABE-treated mice compared to Sham-treated mice (Figure 1). Sham-treated mice experienced spontaneous seizures and succumbed to seizure-induced death by P65. In contrast, in SCN8A-ABE treated mice seizures were completely inhibited in 7 of the 11 mice. In 3 mice spontaneous seizures were significantly reduced in frequency (Figure 2). Hyperexcitability of layer IV/V somatosensory neurons observed in Sham-treated Scn8aW/+-EMX1 mice was attenuated in SCN8A-ABE treated mice. Increases in the pathological persistent sodium current (INaP) were also attenuated to wild type levels in SCN8A-ABE treated mice. Additionally, SCN8A-ABE treatment significantly improved both locomotor activity and anxiety-like behavior comorbidities. These effects were achieved by approximately 30% conversion of mutant to wildtype SCN8A transcripts with no significant off-target editing observed.
Conclusions:
Our results show that ABE treatment successfully reduced the pathogenic phenotype of SCN8A DEEs. We provide compelling evidence that base editors can serve as an effective and targeted therapeutic approach for one SCN8A DEE variant, R1872W, validating the potential for targeted treatment of epilepsies with monogenetic etiologies.
1. Møller, R. S. & Johannesen, K. M. Precision Medicine: SCN8A Encephalopathy Treated with Sodium Channel Blockers. Neurother. J. Am. Soc. Exp. Neurother. 13, 190–191 (2016).
2. Bunton-Stasyshyn, R. K. A. et al. Prominent role of forebrain excitatory neurons in SCN8A encephalopathy. Brain 142, 362 (2019).
Funding:
NS103090, NS122834, NS120702, NS134264.