Genetics of epilepsy syndromes in families with photosensitivity

OBJECTIVE: To use family studies to investigate the clinical genetics of photosensitivity to understand the interrelationship of different photosensitive epilepsy syndromes. METHODS: Twenty-nine families were recruited in which at least 2 members had idiopathic epilepsy and either clinical or electrical photosensitivity on EEG studies. We performed electroclinical analysis of these individuals and all other affected family members and analyzed the phenotypic patterns in families. RESULTS: An earlier age at seizure onset was observed in photosensitive patients compared with nonphotosensitive individuals. A significant female bias for photosensitivity was confirmed. All subjects with visual seizures were photosensitive. Subjects could be classified into 3 main photosensitive phenotypes: genetic (idiopathic) generalized epilepsies (GGE), idiopathic photosensitive occipital epilepsy (IPOE), and mixed GGE/IPOE. Within each category, subjects with purely photosensitive seizures were observed. We report a distinctive syndrome of early-onset photosensitive absence epilepsy, with onset beginning by 4 years of age, which was more refractory than childhood absence epilepsy. CONCLUSIONS: The clinical genetics of the idiopathic photosensitive epilepsies show a phenotypic spectrum from the GGEs to IPOE with overlap between the focal features of IPOE and all the GGE syndromes. Shared genetic determinants are likely to contribute to the complex inheritance pattern of photosensitivity, IPOE, and the GGEs.