Carrying two genes linked to epilepsy may actually make you less likely to have a seizure, say US researchers.
Seizures are caused by bursts of electrical activity
People who have more than one gene defect might be expected to be more prone to illness - but experts found the reverse.
The Baylor College of Medicine team, which carried out its research on mice, reported its findings in the Nature Neuroscience journal.
More than 450,000 people in the UK suffer from some form of epilepsy.
There are many different types of epilepsy and the degrees of severity vary widely from patient to patient.
Scientists have long suspected that some cases are partly due to a genetic problem and are searching for the particular genes involved so that new treatments can be devised.
The two defects highlighted by this research involve the Kcna1 gene, which is involved in the transport of the chemical potassium in and out of the body's cells, and the Cacna1a gene, which plays a role in calcium levels.
The first of these has been linked to severe seizures in "temporal lobe" epilepsy, which affects the part of the brain involved in speech, sight, sound and memory.
Mice with defective Kcna1 genes can die suddenly as a result.
The second gene is linked to so-called "absence" epilepsy, in which patients do not jerk or move in the way most people associate with an epileptic fit but stare into space instead.
When mice were bred with both gene defects, far from worsening their symptoms, they suffered dramatically reduced seizures and did not die suddenly.
The researchers, led by Dr Jeffrey Noebels, said that this could help point towards new ways of treating certain types of epilepsy.
He suggested that one defect could be acting as a "circuit breaker", halting the chain reaction of misplaced electrical signals which can cause a seizure.
"In the genetics of the brain, two wrongs can make a right," he said. "If you have a potassium channel defect, then a drug blocking certain calcium channels might also benefit you."
Professor Sanjay Sisodiya, from the National Hospital for Neurology and Neurosurgery, said that this was the first instance he could think of in which two gene defects in epilepsy combined to reduce symptoms.
He said: "It's quite exciting research - although it demonstrates just how complex the genetics of epilepsy are.
"Hopefully it will all start to come together at some point soon."
A spokesman for the charity Epilepsy Action said: "Any research which could possibly eventually lead to new treatments is exciting and we welcome it."