Is photosensitive epilepsy less common in males due to variation in X chromosome photopigment genes?

Photosensitive epilepsy is less frequent among males than females. Red is the most epileptogenic color. The X-linked red pigment gene contains the polymorphism Ser180Ala; the Ser180 allele increases red sensitivity. We hypothesized that the paucity of males with photosensitive epilepsy is explained by the distribution of this sex-linked allele, and predicted photosensitive males would have a low frequency of this allele. We genotyped 35 males with photosensitive epilepsy and 84 male controls. Allele frequencies did not differ between these groups. The hypothesis was not supported, so alternate reasons for the sex bias in photosensitive epilepsy must be sought.