TWIN BIRTH IS NOT A RISK FACTOR FOR SEIZURES

There is a belief that perinatal factors are a major cause of epilepsy . We studied a community-based sample of twins, a group with a marked excess of adverse perinatal events. The observed number of nontwin sib lings with seizures did not differ from that predicted by the age-spec ific cumulative incidence rate of seizures (4.2% at age 10 years) in t he twins. The types of epilepsies in the twins were largely benign and self-limited and not those associated with brain damage. Zygosity, bi rth order, and birth weight did not predict affected status. Within af fected sibships, the frequency of seizures in co-twins of dizygotic pr obands (9%) was not different from the frequency in nontwin siblings ( 12%) but was much less than the frequency in co-twins of monozygotic p robands (38%; p < 0.001), reflecting a major genetic component to cert ain epilepsies. These data show that twins do not have an increased ri sk of seizures and strongly suggest that perinatal factors have little bearing on the etiology of the common epilepsies in the community.