Causes

The cause of a seizure is determined in about 28% of partial epilepsy patients. In the rest, however, epilepsy is deemed idiopathic, which means that the cause is unknown. The age of seizure onset can sometimes offer a clue. Idiopathic epilepsy is rare in children and young adults.

General Biologic Mechanisms Involved with Seizures

Epileptic seizures are triggered by abnormalities in the brain that cause a group of nerve cells in the cerebral cortex to become activated simultaneously, emitting sudden and excessive bursts of electrical energy. A seizure's effect depends on the location in the brain where this electrical hyperactivity occurs. Effects range from brief moments of confusion to minor spasms to loss of consciousness.

Ion Channels. Sodium, potassium, and calcium act as ions in the brain. They produce electric charges that must fire regularly in order for a steady current to pass from one nerve cell in the brain to another. If the ion channels that carry them are genetically damaged, a chemical imbalance occurs. This can cause nerve signals to misfire, leading to seizures. Abnormalities in the ion channels are believed to be responsible for absence and many other generalized seizures.

Neurotransmitters. Abnormalities may occur in neurotransmitters, the chemicals that act as messengers between nerve cells. Three neurotransmitters are of particular interest:

• Gamma aminobutyric acid (GABA), which helps prevent nerve cells from over-firing.
• Serotonin's role in epilepsy is also being studied. Serotonin is a brain chemical that is important for well-being and associated behaviors (such as eating, relaxation, and sleep). Imbalances in serotonin are also associated with depression.
• Acetylcholine is a neurotransmitter that is important for learning and memory.

Genetic Factors

Dozens of genetic syndromes representing a variety of seizure patterns may account for the different forms epilepsy.

A genetic cause has been identified for at least some cases of juvenile myoclonic epilepsy, which represents 10% of all epilepsy cases. (Such research and other studies have pointed to the GABA signaling system as an important player in many cases of epilepsy.)

Febrile Seizures and Vaccination-Related Seizures

Febrile seizures are caused by high fever and occur in 2 - 5% of children ages 6 months to 5 years. They usually have no long-lasting effect. There are two types of febrile seizures: simple and complex. Simple febrile seizures last for less than 15 minutes and occur once in a 24-hour period. Complex febrile seizures last longer than 15 minutes and occur more than once in 24 hours. Most children who experience simple febrile seizures have a low risk of developing epilepsy.

In young children, high fever from a vaccination can, in rare instances, trigger seizures. These seizures are almost always temporary and have no serious consequences.