Epilepsy

EPILEPSY

Epilepsy and Inheritance

Some people have epilepsy as a result of damage to the brain through, for example, injury, infection, birth trauma, stroke (symptomatic epilepsy). Others, however, have no known or identifiable cause, but have epilepsy as a result of being born with a low epileptic seizure threshold (idiopathic epilepsy). Everyone has a seizure threshold: having a low seizure threshold means that a person has a lower resistance to seizures than people in general. The factors influencing the probability of a person developing epilepsy are the level of the seizure threshold and the severity of any damage to the brain.

There are three different ways in which epilepsy can be ‘inherited’:

• The low epileptic seizure threshold is passed to the next generation through the genes;

• There are a number of medical conditions where the incidence of epilepsy is higher than in the general population;

• There are certain types of epilepsy where a family history has been identified. These include:

• Benign Rolandic Epilepsy

• Some partial epilepsies

• Infantile convulsions

• Juvenile myoclonic epilepsy

• Temporal lobe epilepsy

As the subject of whether epilepsy can be inherited is so complex, anyone with concerns should seek advice from their GP or consultant who may be able to arrange a referral to a genetic counselor. The genetic counselor will collate and consider information such as who in the family has epilepsy or a history of the condition, the seizure type, age of onset, EEG results, and any other medical conditions there may be in the family.

What is the chance that my offspring will have seizures?

For each class of seizure disorder (unprovoked seizures, febrile convulsions, and any seizure), risk is substantially higher in offspring of affected mothers than in those of affected fathers. Risk is either the same or slightly higher in offspring of affected fathers than in the general population...

Why is the risk higher in offspring of affected mothers?

The answer to this question is unknown. The higher seizure risk in offspring of affected mothers is not consistent with any conventional genetic model and it does not appear to be caused by seizure occurrence during pregnancy, use of AEDs [anti-epileptic drugs] during pregnancy, or complications of pregnancy in women with epilepsy.

Does the risk in offspring depend on the type of epilepsy in the parent?

Certain clinical features of epilepsy do appear to be associated with differences in the risk for seizures in offspring. Risk for unprovoked seizures is higher in offspring of parents with onset of epilepsy before 20 years of age than in offspring of those with later ages of onset (9 per cent vs. 3 per cent). Risk is also higher in offspring of parents with a history of absence seizures (9 per cent) than in offspring of those with other generalized (3 per cent) or partial (5 per cent) seizures. Finally, higher risks have been reported in offspring of a proband with idiopathic epilepsy, or of a proband with an effected parent or sibling.

Despite the increased risk for seizures in offspring of parents with epilepsy, patients may be reassured to find that the probability that a child will be unaffected is much higher than the probability that the child will have seizures. Even for patients in the highest risk categories (e.g., women with epilepsy, individuals with absence seizures, or individuals with early age of onset), the probability that an offspring will be completely seizure-free is greater than 80 per cent, the probability that the child will escape having epilepsy is greater than 90 per cent.

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