Seizure risk in offspring of parents with generalized versus partial epilepsy.

Genetic factors are commonly assumed to play a more important role in generalized than in partial epilepsy. This study tested this hypothesis by comparing risks of unprovoked seizures in offspring of individuals with generalized versus partial epilepsy. Overall, seizure incidence was no higher in offspring of persons with generalized epilepsy than in offspring of those with partial epilepsy. The number of affected offspring was about three times that expected from population incidence rates, regardless of whether the parent had partial or generalized epilepsy. For the subgroup of generalized cases with absence seizures, however, seizure incidence in offspring was about three times as high as for partial cases. The higher incidence in offspring of absence cases was only partly explained by a higher proportion of absence than partial cases with two factors associated with high risk in relatives, namely early age at onset and idiopathic epilepsy. Offspring of absence cases had higher risk than offspring of other cases not only for absence seizures, but for other seizure types as well, suggesting that absence epilepsy is not genetically distinct from other seizure types of epilepsy. These results suggest that the higher incidence sometimes observed in relatives of patients with generalized epilepsy is due to a small proportion of generalized cases with extremely high familial risks--most generalized epilepsies are no more likely than partial epilepsies to have a genetic basis.