Male monozygotic twins discordant for periventricular nodular heterotopia and epilepsy

Purpose: To determine zygosity and study cerebral structure in apparently i dentical twins with discordant manifestation of focal epilepsy. Methods: Male twins in their fifth decade were scanned by using magnetic re sonance imaging (MRI) to detect structural abnormalities. Zygosity was dete rmined by using 10 microsatellite markers, Results: DNA analysis showed that the twins were >99.99% likely to be monoz ygous; they were discordant for bilateral symmetric periventricular nodular heterotopia (PNH) and epilepsy. Conclusions: The discordant occurrence of PNH and epilepsy in monozygotic m ale twins carries implications with respect to somatic mosaicism, currently held to be responsible for PNH In affected male subjects.