Symptomatic epilepsy has a known cause, such as meningitis, stroke, or brain damage during a difficult birth. Idiopathic epilepsy, which occurs in approximately six out of ten patients, has no known cause.
The tendency to have seizures, a low seizure threshold, may run in families. Some types of epilepsy, such as juvenile myoclonic epilepsy are now believed to be inherited. Additionally, some inherited syndromes have epilepsy as a symptom.