One-hundred and seventy-nine offspring of 120 probands with a history of febrile convulsions (FC) were studied to determine the risk of seizures and possible factors influencing this risk. The conditions for this study were especially good since all of the probands had undergone clinical and EEG examinations as well as an assessment of family history of seizures during childhood. Hence, for the first time the seizure status of the probands' parents could be included in the calculation of risk in offspring. In sibs the risk was highest if the mother of the proband had experienced seizures (20% vs 9% in offspring of probands with nonaffected parents). Similarly, offspring of probands with affected mothers had a much higher risk (27%) than offspring of probands with affected fathers (7%). Our findings point to a maternal preponderance in the transmission of FC liability. No relationship was found between the presence of EEG traits of a genetic seizure liability (theta rhythms, spikes and waves, photoparoxysmal response, focal sharp waves) in probands during childhood and the seizure risk in their offspring. The present data provide no basis for forming an hypothesis regarding the possible mode of inheritance of FC. This is not surprising since FC as already shown in the EEG-are not a homogeneous disorder, but are caused by a variety of genetic factors occurring in variable constellations. Possibly, in a subgroup of probands with seizure affected mothers the susceptibility to FC follows a multifactorial polygenic mode of inheritance.
Conclusion: The seizure incidence in offspring of individuals with a history of FC was 10% (only FC in 64% of the affected offspring). Offspring of females with affected parents were at an increased risk. Pathological childhood EEG findings of the probands were not related to an increased risk in offspring.