[Polymorphic expression of epilepsy and cognitive impairment in ring chromosome 20 syndrome].

Ring chromosome 20 syndrome combines epilepsy with varying levels of mental retardation, behavioral disorders, and malformations. Epilepsy is generally serious, with frequent drug resistance. The pathophysiology of seizures remains unclear. Rearrangements of two epilepsy genes, CHRNA4 and KCNQ2, have been raised as the cause. We report the observation of one child, with a telomeric deletion 20p13, with no epileptic symptoms. Preservation of CHRNA4 and KCNQ2 gene activity could explain this distinctive feature.