[Ring chromosome 20: an epileptic channel disorder?].

INTRODUCTION: The ring-shaped chromosome 20 (r20) syndrome is an infrequent chromosopathy which is associated with epileptic seizures, behaviour disorders and mental retardation. It results from the fusion of the two arms of the chromosome with deletion of the telomeric portions.

CLINICAL CASE: We present a case of r20, review published cases and describe the clinical and neurophysiological characteristics.

CONCLUSIONS: The r20 syndrome is the third type of epilepsy known to be of genetic basis related to chromosome 20. It has clinical and neurophysiological characteristics which give it a distinctive character and are easily identified. The fact that on locus 20q13 (telomeric portion of the long arm of chromosome 20) two genes related to epileptic channelopathies (CHRNA4 and KCNQ2) have been described, suggest the hypothesis that the subjacent deletion in cases of r20 syndrome affect one of these genes and explains the epileptogenicity. We consider this hypothesis and the possibility that r20 syndrome may be an epileptic channelopathy.