Path cleared for intractable epilepsy gene therapy — Gunma University deploys new method to suppress seizures in mice

A research group including Assistant Professor Yuuki Fukai and Professor Hirokazu Hirai of the Initiative for Advanced Research at Gunma University has successfully developed cmGAD67, a new gene promoter capable of driving gene expression exclusively in inhibitory neurons of the brain. Utilizing this promoter to conduct gene therapy aimed at boosting the production of the inhibitory neurotransmitter GABA in the brain, the team achieved a significant reduction in seizures across multiple mouse models of epilepsy. Because it can selectively target inhibitory neurons, the approach has the potential to enhance therapeutic efficacy while minimizing side effects. Moving forward, the research group plans to advance validation in primates to realize a gene therapy for intractable epilepsy. The findings were published in Molecular Therapy.

Epilepsy is a neurological disorder characterized by recurrent seizures caused by the excessive excitation of brain neurons, affecting an estimated 50 million people worldwide and approximately 1 million patients in Japan. Although anti-epileptic drugs are available, they are ineffective for about 30% of patients, a condition referred to as intractable epilepsy.

Gene therapy using adeno-associated virus (AAV) vectors to enhance inhibitory neuron function is considered a promising new therapeutic approach. However, conventional inhibitory neuron-specific promoters are large, consuming a significant portion of the AAV vector's limited payload capacity. Furthermore, their expression activity has been insufficient, making it difficult to express the therapeutic gene in the quantities needed to achieve a therapeutic effect.

To overcome this challenge, the research group meticulously analyzed the expression regulatory region of the GAD67 gene (an enzyme that synthesizes the inhibitory neurotransmitter GABA) and developed cmGAD67, an ultra-small promoter that induces selective gene expression in inhibitory neurons. Despite its remarkably short sequence of just 410 base pairs, cmGAD67 demonstrated higher expression activity than conventional inhibitory neuron-specific promoters.

Next, when the characteristics of cmGAD67 were evaluated in the mouse brain using an AAV vector, more than 90% of the gene-expressing cells were inhibitory neurons, confirming high cell-type specificity. It was also found that the promoter could efficiently express genes in major inhibitory neuron subtypes within the brain, including parvalbumin-positive and somatostatin-positive neurons. Furthermore, the team engineered an AAV vector to express GAD65, a GABA-synthesizing enzyme, under the control of cmGAD67, and administered it to multiple mouse models of epilepsy.

As a result, an increase in the amount of GABA in the brain was confirmed, along with a decrease in seizure-related electrocorticogram activity, a reduction in seizure severity, and an improvement in survival rates. No obvious adverse effects on motor function or spontaneous behavior were observed.

These results demonstrate that cmGAD67 is a valuable gene expression control technology capable of selectively targeting inhibitory neurons. Having demonstrated its seizure-suppressing efficacy through gene therapy, it holds promise as an effective new therapeutic strategy for intractable epilepsy.

With an eye toward human clinical application, the research group is currently advancing validations using non-human primates, such as marmosets. They plan to evaluate its efficacy and safety in intractable epilepsy models, accelerating research and development toward clinical application. Additionally, imbalances between excitation and inhibition in the brain are implicated in various neurological disorders beyond epilepsy. cmGAD67 is therefore expected to find broad application in inhibitory neuron-targeted gene therapies and neural circuit research.

Journal Information
Publication: Molecular Therapy
Title: A compact GAD67 promoter enables inhibitory neuron-targeted AAV gene therapy for seizure suppression
DOI: 10.1016/j.ymthe.2026.06.007