The human brain develops through a delicate process where nerve cells grow, move to the right spots, and arrange themselves into functional layers. Abnormalities in this intricate coordination cause malformations in the brain's cortex, leading to focal cortical dysplasia (FCD), the most common cause of epilepsy in children. Patients with FCD are often resistant to anti-epileptic therapy. Surgery to remove the malformed parts of the brain is the standard treatment, which risks altering normal brain function.

In a recent study, researchers at University College London showed that a gene therapy targeted at cortical neurons significantly reduced the frequency of FCD-induced seizures in adult mice (1). “It's proof of concept that gene therapy can work after seizures have started,” said Angeligue Bordey, a neuroscientist at the Yale School of Medicine who was not involved in the study but who also tested an early treatment to correct seizures before they occurred (2).

The researchers focused on developing a gene therapy that could directly address seizures, a symptom common to all patients with epilepsy, regardless of cause. By targeting seizure reduction, they aimed to develop a universally applicable treatment. “If we decrease the seizures in [FCD] patients, we can have a treatment for all [epilepsy] patients,” said Gabriele Lignani, a translational neuroscientist at University College London and study coauthor. 

The gene therapy did the job of an antiepileptic drug but was targeted to a specific brain region to mitigate seizures and minimize the side effects typically associated with systemic medications. “It's a bit of a different way of doing gene therapy, compared to just correcting a mutation that is really specific for a patient and sometimes more specific to the mouse model than to the patient,” Lignani said. 

Lignani’s research team used an existing mouse model of FCD that involves introducing genetic material into the developing brain of mouse embryos using in utero electroporation. They used a plasmid carrying both a fluorescent marker for easy visualization and a constitutively active Ras homolog enriched in brain (RHEB), an activator of the mechanistic target of rapamycin (mTOR) pathway. Overactivation of mTOR resulted in the characteristic features of FCD, including dysmorphic, enlarged, and misplaced neurons. 

To monitor brain activity, the researchers implanted the mice with subcutaneous wireless electrocorticography transmitters positioned over areas showing successful electroporation. This setup allowed for continuous baseline monitoring of brain activity. After 10-15 days of recording, they found that about 65 percent of the electroporated animals exhibited generalized seizures and showed learning disability and impaired social cognition often seen in patients with FCD. 

After establishing baseline seizure activity in the mice, the next step was to evaluate the effect of a gene therapy based on overexpression of the Kv1.1 potassium channel, a type of voltage-gated potassium channel that regulates neuronal excitability. Overexpressing Kv1.1 can enhance the outward flow of K+ ions, making neurons less likely to fire excessively, which is a common problem in epilepsy. “This channel seems quite good at decreasing excitability and decreasing seizures,” Lignani said. 

It's a bit of a different way of doing gene therapy compared to just correcting a mutation that is really specific for a patient and sometimes more specific to the mouse model than to the patient. 
- Gabriele Lignani, University College London

The researchers designed the potassium channel transgene to be most active in the brain’s main excitatory neurons and packaged it in an adeno-associated viral vector (AAV9). Lignani’s team used a cannula to deliver the treatment and monitored brain activity to assess the impact of gene therapy on seizures.

Mice treated with the gene therapy showed a 64 percent reduction in seizures compared to their baselines, with 60 percent of treated animals becoming seizure-free by the end of the observation period. “It's a pretty significant reduction,” said Bordey. “These experiments are very hard to do, so that's an enormous amount of work done.” 

Lignani believes that this gene therapy could be a viable alternative to surgery for patients with epilepsy. “If [gene therapy] works and you don't have seizures, that's it. If it doesn't work, we still have the surgery [to fall back on],” he said. 

This gene therapy also looks promising for patients with FCD in brain regions where surgery is not an option. “It’s less invasive, meaning that you need to make a small hole to inject the virus, instead of taking out a big part of the brain,” said Lignani. 

However, Bordey said that AAV gene therapy comes with its own risks. “Once you put it in, it's there for at least five or ten years,” she said. “If you have a side effect, you're stuck with it.” 

Lignani’s team is gearing up to start a clinical trial in adult patients before expanding to include pediatric cases. This decision is grounded in a comprehensive body of translational preclinical work (3,4). “That gives us assurance that we have a good effect,” he said. “We are quite confident that it works.”

References

1.  Almacellas Barbanoj, A. et al. Anti-seizure gene therapy for focal cortical dysplasia. Brain  147, 542–553 (2023).
2. Hsieh, L. S. et al. Convulsive seizures from experimental focal cortical dysplasia occur independently of cell misplacement. Nat Commun  7, 11753 (2016).
3. Colasante, G. et al. In vivo CRISPRa decreases seizures and rescues cognitive deficits in a rodent model of epilepsy. Brain J Neurol  143, 891–905 (2020).
4. Qiu, Y. et al. On-demand cell-autonomous gene therapy for brain circuit disorders. Science  378, 523–532 (2022).