Gene therapy with a drug 'dimmer switch' cut seizures by more than 90% in three people with drug-resistant epilepsy

Researchers led by neurosurgeon Yang Dai of Xuanwu Hospital, Capital Medical University, Beijing, reported on 4 November 2026 in The New England Journal of Medicine an early-stage trial of a chemogenetic gene therapy for epilepsy, according to Nature.

How it works

• A virus (adeno-associated virus 9) delivers a gene directly into the small patch of brain tissue where seizures start.
• The gene is engineered to act in excitatory neurons — the cells involved in seizures — and makes them sensitive to a specific drug.
• The drug then works like a dimmer switch: doctors can adjust the strength of the effect, which is not possible with other kinds of gene therapy. In this trial the drug was the antipsychotic clozapine.

Who took part

Three adults with epilepsy caused by hippocampal sclerosis (scarring) on one side of the brain. They had been diagnosed 10–25 years earlier, were resistant to at least two anti-seizure medicines and had at least two seizures a month on average before enrolling.

Results

In each participant, monthly seizures fell by more than 90%. No serious side effects were reported.

Limitations

• Type: an early-stage clinical trial with only three participants and no control group — far too few to judge safety or effectiveness.
• Independent neurologist Matthew Walker (University College London) called the effect exciting but stressed the small size. He also raised concerns about long-term clozapine use, which at high doses has been linked to cardiovascular and other problems. Walker co-founded Focalis Bio, which is developing epilepsy gene therapies.

This is experimental research, not an available treatment. People with epilepsy should discuss treatment options with their doctor.