Inheritance of photosensitivity

Purpose: To investigate the mode of inheritance of the photoparoxysmal resp onse (PPR) and to obtain more information about the influence of photosensi tivity on the seizure risk in siblings of patients with epilepsy. Methods: Examination of the records of families with one photosensitive par ent (Group I, n = 54) and of families with a photosensitive proband, neithe r of whose parents was photosensitive (Group II, n = 72). Results: At the age of maximum penetrance, between 5 and 15 years of age, 5 0% of the siblings in Group I were photosensitive, compared to only 15% in Group II. Siblings in Group I showed a higher seizure rate (19%) than sibli ngs in Group II (4%, p < 0.005). The majority of photosensitive siblings ha d no seizures, but photosensitive siblings had a higher seizure risk than n on-photosensitive siblings. The highest seizure risk was found in photosens itive siblings of Group 1 (33 %) compared to 9% in non-photosensitive sibli ngs (p < 0.05). Conclusion: Our findings show that a PPR in parents is a major determinant for the risk of a PPR in offspring. The results may indicate an autosomal-d ominant transmission with age-dependent penetrance of the PPR. Photosensiti vity is an important factor in the pathogenesis of seizure disorders in chi ldhood.