The incidence of epilepsy declines over the first 20 years of life and then remains stable until age 55 to 60 years, when there may be an increase, largely related to stroke, brain tumors, and Alzheimer's disease. Further, the causes of epilepsy vary with the age at which seizures develop. Epidemiological studies have failed to establish a clear relationship between vaccination and epilepsy. In some cases, however, vaccination may cause a fever associated with a febrile convulsion. When epilepsy develops at a young age, there is an increased risk of epilepsy among the brothers and sisters and the affected person's children.
Genetic factors are more commonly present in primary generalized epilepsy than in partial epilepsy.
Among individuals with partial epilepsy in whom a clear cause of seizures can be identified, such as serious head injury with loss of conscious ness for longer than a day, there is evidence that the chance of developing epilepsy may be influenced by heredity. The rate of seizures is higher among the family members of people who develop epilepsy after head trauma than among the relatives of people who do not. There is an increased risk of epilepsy in children of parents with epilepsy. Epilepsy is roughly twice as common among the children of women with epilepsy than among the children of men with epilepsy. In most cases where heredity is important, a single gene is not considered to be the sole determining factor.