Monozygous twin brothers discordant for photosensitive epilepsy: first report of possible visual priming in humans.

Purpose: The interaction of genetic predisposition and the environment in the development of epilepsy is often discussed, but, aside from some animal reflex epilepsies, little evidence supports such interaction in the development of reflex epilepsy in humans.

Methods: We describe the history of a 16-year-old boy in whom photosensitive epilepsy developed after a period of weekly exposures to high-intensity light flashes.

Results: Both he and his clinically unaffected monozygotic twin were found to be photosensitive.

Conclusions: This case report suggests that some genetic forms of human reflex epilepsy may be elicited by repeated environmental exposure to the appropriate stimulus, similar to some of the stimulus-induced epilepsies seen in animals.