Causes of epilepsies: Insights from discordant monozygous twins

Whereas some patients with epilepsy have known acquired or genetic causes, in many the cause is unknown. By analyzing monozygotic twins, discordant fo r epilepsy, subtle etiological factors may be detected. We analyzed 12 mono zygotic, discordant twins for factors explaining discordancy. These factors were presence of major clinical risk factors, presence of possibly epilept ogenic lesions on brain magnetic resonance imaging (MRI), and quantitative brain volume abnormalities. Major risk factors, with associated acquired le sions were found in 4 of 12 twins. An MRI lesion without a major risk facto r was found in a further 4 of 12 twins. Two of these had unilateral malform ations of cortical development, 1 had bilateral periventricular heterotopia , and 1 had focal atrophy. Significant twin-twin differences in MRI volumes without obvious MRT lesions or major risk factors were found in 2 of 12 tw ins.:Both had larger volumes than their co-twins, and idiopathic generalize d epilepsy. No clinical or MRT findings accounting for discordance for epil epsy were found in 2 of 12 twins. In 10 of 12 pairs a clinical or MR correl ate of epilepsy was found; some of those were subtle and only apparent by t win-twin comparison. They may be due to occult acquired factors, such as pr enatal insults, or to genetic abnormalities resulting from postfertilizatio n genetic processes.