CHOP Researchers Advance Understanding and Treatment of Childhood Epileptic Disorders

By Lauren Ingeno

Using an advanced genome-editing approach, Children’s Hospital of Philadelphia researchers are investigating a gene therapy to treat Dravet syndrome, a genetic disease that causes a severe form of epilepsy.

The project, funded by the Dravet Syndrome Foundation, builds off of years of basic science research from the laboratory of Ethan Goldberg, MD, PhD, an Associate Professor in the Division of Neurology at CHOP and director of the Epilepsy Neurogenetics Initiative (ENGIN) Frontier Program.

“The technique we’re using, called base editing, is able to generate mutations at very specific locations in the genome without forming a double-stranded DNA break,” Dr. Goldberg said. “This research will be a proof of principle to see whether this technology could be applied to a genetic epilepsy in a pre-clinical model.”

Dravet syndrome affects about 1 in 16,000 infants in the United States, making it the most common epileptic encephalopathy. Starting in the first year of life, patients experience severe seizures, as well as intellectual and developmental disability, and a high rate of autism.

“Medications can reduce the frequency of seizures, but in most cases, they can't eliminate them,” Dr. Goldberg said. “And those medications have no effect on the developmental delay, intellectual disability, and autism spectrum disorder that patients with Dravet syndrome experience.” 

The disorder is caused by variants in the SCN1A gene, which provides instructions for making the brain’s sodium channels. SCN1A is preferentially expressed in a type of neuron called an inhibitory interneuron. When inhibitory interneurons are active, they work like an anti-seizure control system by silencing the cells around them. In Dravet syndrome, the brain is unable to control neuron activity, which is thought to increase seizures.

In earlier research, Dr. Goldberg and colleagues discovered that while these interneurons were dysfunctional early in the disease course of Dravet syndrome, they normalized by young adulthood in an animal model. In 2022, the researchers showed that while small animal models of Dravet syndrome continue to experience seizures into adulthood, these interneurons recover their ability to fire electrical discharges, and their signal does not propagate down to the synapse to impact other cells downstream.

With renewal of R01 funding from the National Institutes of Health, the Goldberg Laboratory will continue to investigate the mechanistic underpinnings of Dravet syndrome while concurrently studying gene editing as a potential therapeutic strategy for the disease.

Base Editing: A More Precise CRISPR Tool

CRISPR/Cas9 is a Nobel Prize-winning gene editing technology that uses a guide RNA to target a specific DNA sequence and directs an enzyme (Cas9) to chemically cut and modify the genetic code. CRISPR/CAS9 cuts through both DNA strands, which allows for new DNA to be added or removed at the target site but can lead to unintended and harmful changes to the genome. 

To circumvent these off-target “bystander” effects of CRISPR/Cas9, molecular biologist and chemist David R. Liu, PhD, a faculty member at MIT and Harvard University, pioneered a new version of CRISPR called “base editing” in 2016. Base editing can rewrite individual DNA letters, or bases, in the genome without making double-stranded DNA breaks. The technology was named a Science 2017 Breakthrough of the Year finalist and is being investigated in 11 clinical trials to treat diseases — from leukemia to sickle cell disease.

Dr. Liu has now teamed up with Dr. Goldberg to develop and apply a base editing strategy for Dravet syndrome in a validated preclinical model.

“Base editing is an improvement on CRISPR/Cas9 by avoiding double-strand breaks and reducing the risk of off-target mutations, and it can be applied in non-dividing cells,” Dr. Goldberg said. 

To test base editing as a potential treatment — or even a preventive measure — for Dravet syndrome, Dr. Goldberg and his team at CHOP, led by Postdoctoral Fellow Sophie F. Hill, PhD, will investigate the therapy’s ability to prevent febrile seizures, epilepsy, and mortality in animal models of the disease, and to reverse the abnormalities seen in inhibitory neurons. 

“Our preliminary data suggests that we have an over 95% reduction in mortality when we treat at birth with this base editor and at least partial correction of the abnormal electrical activity in these SCN1A-expressing interneurons,” Dr. Goldberg said.

Understanding Temperature-Induced Seizures

As a final piece of the Dravet syndrome puzzle, Dr. Goldberg was awarded NIH funding to study febrile seizures, which happen in young children as the result of a high fever. While all patients with Dravet syndrome experience febrile seizures, they are also the most common type of seizures among the general population, occurring in up to 4% of all children. Yet, febrile seizures mysteriously vanish once children reach kindergarten age.

While most febrile seizures are benign, they can also be a risk factor for future epilepsy and are a known cause of sudden infant death. Despite the prevalence and potential severity of febrile seizures, the mechanism behind them is poorly understood. 

“If you treat a child with recurrent febrile seizures with an antiseizure medicine, it has no effect, suggesting that the mechanism of febrile seizures and epilepsy are different,” Dr. Goldberg said.

Dr. Goldberg and his research team, led by Postdoctoral Fellow Eric R. Wengert, PhD, are now using their previous discoveries about the underpinnings of Dravet syndrome to better understand why the developing brain is vulnerable to temperature-induced seizures.

“We believe this research could potentially lead to an actual treatment for recurrent febrile seizures,” Dr. Goldberg said.

Combined, funding from the NIH and the Dravet Syndrome Foundation will help the Goldberg Lab better understand the mechanisms of epilepsy during childhood that could one day lead to preventative or curative therapies in kids with Dravet syndrome, as well as seizures of childhood in general.