Scientists discover dual-gene pathway behind half of unexplained epilepsy cases

Half of all people with epilepsy walk into a clinic with a mystery. They have seizures. Genetic testing suggests something is wrong in their DNA. But the tests come back empty. No single faulty gene. No clear diagnosis. No obvious path to treatment. For decades, this silence has frustrated patients and researchers alike—until now.

Scientists at Baylor College of Medicine and the Duncan Neurological Research Institute have identified why. Epilepsy, they found, does not always announce itself through a single broken gene. Sometimes it arrives quietly, the result of two defective genes working together in ways no one had fully understood. The discovery, published in the Journal of Clinical Investigation, offers a framework for diagnosing and potentially treating roughly half of the fifty million people worldwide who live with epilepsy—the ones whose seizures have no name.

The traditional view held that seizures came from disruption in one of over a thousand known epilepsy genes. Researchers had mapped many of them. They understood that most affected the way neurons communicate, flooding the brain with too much electrical activity. But this model left a gap. More than half of patients with suspected genetic epilepsy had no diagnosis. Their genes seemed fine when examined one at a time. Something else was happening.

Dr. Shenzhao Lu and his team decided to look at a different class of genes—ones involved in actin, a protein that forms the structural scaffolding inside every cell. Actin filaments are like tiny construction blocks, building and reshaping the cell's skeleton. In 2022, Lu's group had found the first link between defects in a human gene called TIAM1 and seizures. TIAM1 helps neurons build these actin filaments. When it breaks, something goes wrong. But what?

Using fruit flies as a model, the researchers bred flies with a defective version of the TIAM1 equivalent. The flies seized. Under the microscope, their neurons showed actin filaments that were shorter and clumped together compared to normal flies. Yet when Lu looked at the neurons' structure and connections, they appeared normal. The wiring was fine. So why the seizures? The answer lay deeper, in the cell's power plants. Neurons with broken actin filaments had more mitochondria than normal—and these mitochondria were smaller and working harder. They were churning out excessive amounts of reactive oxygen species, or ROS, the toxic byproducts of cellular energy production. Too much ROS triggered a cascade: increased activity in glutamate-producing neurons, the brain's main excitatory messenger, and then seizures.

The team called this the actin-mitochondria-glutamate pathway, or AMG. It was a new way to think about seizures. When they blocked parts of this pathway in flies—using a drug that prevented mitochondrial fragmentation, or another that mopped up excess ROS—the seizures stopped. More striking still, when the researchers looked at patients with unexplained epilepsy, they found more defective AMG genes in their DNA than in people without the condition. Combining two broken genes from this pathway, they discovered, was enough to trigger seizures in the fruit fly model. Many of the gene pairs found in actual patients did the same.

The implications are immediate. Doctors can now test for combinations of defective genes rather than hunting for a single culprit. Patients who have spent years without answers may finally get a diagnosis. And the pathway itself suggests new targets for drugs—ways to stabilize mitochondria, reduce oxidative stress, or calm overactive neurons. For the millions living with seizures that medicine has never explained, this is the beginning of an answer.