Lennox’s original files of twins with seizures from 1934 through 1958 were reviewed, and the International League Against Epilepsy (ILAE) classifications of seizures and epileptic syndromes were applied to 143 (71 monozygous [MZ], 72 dizygous ) twin pairs, in a study at the University of Melbourne, Australia; the Montreal Neurological Institute, Canada; Harvard Medical School, and Beth Israel Medical Center, Boston, USA. The Lennox data that included personal records and EEGs allowed classification of 75% of cases according to contemporary ILAE epilepsies and epileptic syndromes. “Petit mal” corresponded to the contemporary absence seizures, and “psychomotor seizures” equated with simple and complex partial terminology. For MZ and DZ twin pairs, concordance for seizures was 59% and 14%, respectively. Casewise concordance estimates for MZ and DZ twin pairs showed a strong genetic influence in idiopathic generalized epilepsies. High MZ concordances also supported a genetic etiology in symptomatic generalized epilepsies and febrile seizures. In the Lennox data 86% of MZ twin pairs and 60% of DZ twin pairs were concordant for both seizures and epilepsy syndromes. The Australian data showed 94% of MZ and 71% of DZ twin pairs were concordant for epilepsy syndromes. Also, a genetic contribution to partial epilepsy was evident although weaker than that for generalized epilepsies. 
COMMENT. Despite the differences in epilepsy terminology, the earlier Lennox and recent Australian twin studies provide similar and valuable evidence of a genetic basis for generalized epilepsies and febrile seizures and further support the concept of specific genes for epilepsy syndromes. A genetic factor in symptomatic generalized epilepsies demonstrated in the twin studies is also apparent in a current Japanese study of family history rates of epilepsy and consanguinity . In 311 probands with childhood-onset epilepsy, a family history of epilepsy (within second-degree relatives) occurred in 19% and consanguinity (within first-degree relatives) in 6%. A positive family history was more common with generalized than localization-related epilepsies, and more common with idiopathic/cryptogenic epilepsy than symptomatic epilepsy. However, the data suggest that a genetic susceptibility could play a role in the etiology of pre- or perinatal symptomatic generalized epilepsy and in postnatal symptomatic localization-related epilepsy. Also, a genetic factor through consanguinity may influence the etiology of idiopathic/cryptogenic and symptomatic generalized epilepsies.