Abstracts

The incidence of febrile seizures (FS) is estimated to be between 2 and 5% in North America and Europe. Complex febrile seizures (CFS) including status epilepticus (FSE) are estimated to occur in 20 to 35% of these children with approximately 5% being FSE. Although FS are generally benign, up to 5% go on to develop later seizures, wtih CFS, specifically FSE, having a greater risk of developing epilepsy. The occurrence of FS in first and second degree relatives has also been found to be associated with an increased risk of epilepsy. Utlizing data from the Middle Atlantic Twin Registry (MATR), Norwegian Twin Panel (NTP) and the Danish Twin Registry (DTR), affected twins and relatives were classified as having FS (simple (SFS), CFS, FSE), as well as epilepsy. Medical information, including seizure history, was available on a total of 47,626 twin pairs ascertained from the three registries (17,112 MATR, 13,691 NTP, 16,823 DTR). Data was obtained through questionnaires and interviews with verification through medical records. Febrile seizures were validated in a total of 1,745 twins or family members. SFS or FS of unknown origin accounted for the largest proportion of cases identified (1,393, 79.8%). Total CFS equaled 352 (20.2%) with FSE in 119 (6.8%). Epilepsy was verified in 73 SFS or unknown cases (5.2%), while 43 were found to have had epilepsy following CFS (12.2%) and 19 of 119 subsequent to FSE (16%). In MZ twins with FSE, 8 of 18 developed epilepsy, whereas this was the case in only 5 of 46 DZ twins. The proportion is significantly increased in MZ twins compared to DZ twins (p=0.0026). These results verify that most cases of FS are benign and do not progress to epilepsy. A higher incidence of epilepsy followed CFS, especially in those with prior FSE. Clustering of FSE and epilepsy in some families, particularly in MZ twins, suggests a genetic component as a partial etiology. (Supported by Grants from the National Institutes of Health NINDS (NS25630 and NS31564).)