Genetic and developmental influences on susceptibility to epilepsy: evidence from twins.

This study evaluated genetic and developmental contributions to epilepsy, using data on epilepsy and multiple births in the sibships of 1981 probands with epilepsy. Prevalence of a history of epilepsy was much higher in monozygotic (MZ) than in dizygotic (DZ) co-twins of probands (35.0% vs. 3.7%), but prevalence was not significantly higher in DZ co-twins than in singleton siblings. The proportion of individuals who were MZ twins was higher among probands with epilepsy than among their non-co-twin siblings without epilepsy (odds ratio 2.5, 95% CI 1.31-4.85). However, the proportion who were DZ twins was similar among probands and unaffected siblings (odds ratio 1.0, 95% CI 0.67-1.60). These findings suggest that the increased prevalence of epilepsy in MZ co-twins of probands may be partly explained by developmental factors related to MZ twinning, rather than by their genetic identity with the probands.