The risk of seizure disorders among relatives of children with febrile convulsions.

We studied the risk for seizure disorders among relatives of probands with febrile convulsions. The risk for febrile convulsions was raised in siblings, offspring, and nieces and nephews of probands. Risks to siblings were higher if one or both parents also had febrile convulsions, or the proband had no identified neurologic abnormality before the febrile convulsion, if the proband had recurrent febrile convulsions, or the febrile convulsions were complex. The risk for epilepsy was raised in siblings of probands, but not in other relatives. If the proband had febrile convulsions followed by epilepsy, risk to siblings for febrile convulsions and for epilepsy was significantly higher than when probands had either condition alone.