A Rare Cause of Epilepsy In A Child: Mosaic Ring Chromosome 21

Introduction: Ring chromosome is a structural chromosomal abnormality, and is seen with a frequency of 1 / 30,000-60,000. The association of ring 14, 17 and 20 with epilepsy or epileptic syndromes are well-defined. Refractory complex partial seizures, nocturnal frontal lobe epilepsy, non-convulsive status epilepticus were reported in more than 90% of the patients. Ring chromosome 21 is reported less frequently than other ring chromosomes and rarely accompanied by epilepsy Case Report: An 11-year-old boy was brought to the pediatric neurology outpatient clinic because of history of generalized tonic-clonic seizures. On his physical examination when he was 5 months old, he had barchycephaly, bilateral epichantus and blepharophimosis, flat nasal bridge, long philtrum, uplift ear lobes, overriding 2nd and 4th fingers of the feet, overlapping the 2nd and 4th toes. Karyotype and array-CGH analysis revelaed a 5.5 Mb duplication of the 21q22.12q22.3 region, and a 4.9 Mb pure deletion of the 21q22.3 region (arr[hg19] 21q22.12q22.3(37,439,289-42,911,329)~3,21q22.3(43,205,976-48,084,156)x1) compatible with mosaic ring chromosome 21. Valproic acid was started and gradually increased as planned. The sleep EEG and cranial MRI were uneventful. The patient was seizure-free at the last follow-up 10 months after admission under valproate treatment (20mg/kg/d). Discussion: Ring chromosome 21 is a rare abnormality and as in our patient it may be associated with epilepsy. We presented our patient to emphasize the importance of the determination of the genetic basis of epilepsy and epileptic syndromes without structural anomalies to understand the pathogenesis of epilepsy.