Neurogenetics and Gene Therapy: Forget the Mouse: The Future of Pre-Clinical Trials in Neurogenetic Disease*

Sudden Unexpected Death in Epilepsy (SUDEP) is a leading cause of death in epilepsy patients. While SUDEP mechanisms are not understood, there is evidence to implicate apnea, autonomic dysfunction, and cardiac arrhythmias. Variants in SCN1A are linked to Dravet syndrome (DS). DS patients have the highest SUDEP risk, up to 20%. There are few effective therapies for any of the genetic epilepsies and no reliable biomarkers for SUDEP risk. Importantly, SCN1A is expressed in heart and brain in humans and rodents. Thus, we proposed that cardiac arrhythmias contribute to the mechanism of SUDEP in DS. Rabbits more closely replicate the human cardiac action potential than mice. We generated a rabbit Scn1a deletion model using CRISPR-Cas9 gene editing. Rabbits are optimal models to investigate neuro-cardiac mechanisms of SUDEP as well as to develop novel therapeutics for DS. To our knowledge, this is the first transgenic large animal model of a DEE.

MELAS and LHON-Plus are intractable, progressive, and multi-systemic mitochondrial diseases with no effective therapeutic intervention. They are caused by maternally inherited mitochondrial variants impairing the oxidative phosphorylation pathway responsible for ATP synthesis. They share a molecular etiology with a Complex I deficiency and chronic energy deficit that affect organs with high energy demands and a dependence on aerobic metabolism. Patients with MELAS or LHON-Plus exhibit overlapping and divergent phenotypic manifestations. It is in the clinical context of their multi-systemic phenotypes that we designed a pharmaco-epigenomic approach to induce mitochondrial metabolic reprogramming to bypass the deficient Complex I and curtail ATP deficiency. The absence of a MELAS or LHON-Plus animal model makes patient-derived fibroblasts the only feasible ex vivo diseased paradigm to test therapeutic candidates during IND enabling studies. We show that our investigational drug induces mitochondrial metabolic reprogramming and ATP output to avert an ATP crisis during high energy expenditure.

Protocadherin-19 (PCDH19)-clustering epilepsy (PCE) is a severe developmental and epileptic encephalopathy (DEE), characterized by early onset of intractable seizure clusters and cognitive impairment. PCDH19 is an X-linked gene, but PCE affects females and rare mosaic males, while hemizygous males do not develop epilepsy. This is thought to be due to random X-inactivation, leading to a mosaic pattern in which cells expressing wild type or mutant PCDH19 fail to interact properly during brain development. Our mouse model of PCE shows a striking pattern in which the Pcdh19+ and null neurons segregate from one another in the cortex, hippocampus, and interneuron progenitors in the ganglionic eminences. Additionally, PCE mice have a lower seizure threshold when exposed to hyperthermia. Brains of PCE mice showed a decreased density of parvalbumin interneurons when compared to wild-type controls, suggesting that alterations in inhibitory interneuron distribution may be an underlying factor in the phenotypic spectrum of PCE.

During the talk I will discuss our recent findings on the functional ramifications of TDP-43 splicing alterations on neuronal excitability and focus on our efforts to design rational therapeutics targeting human specific events that drive pathological dysfunction in ALS.