PP01.5 – 3005: Clinical and cytogenetic features of 3 cases with ring chromosome 20 syndrome

Objective Ring chromosome 20 syndrome (R20) has an almost constant association with refractory epilepsy and intellectual and behavioral disabilities. Though early diagnosis is usually difficult and rarely made, Particular electroclinical patterns have been found to be very helpful for the R20 diagnosis that is usually difficult and rarely early made. Here, we present the clinical, EEG and cytogenetic correlations in three patients with R20. Methods Three patients, aged 17, 13 and 4 years, respectively, were studied by video-EEG monitoring (VEEG) for drug-resistant seizures. Brain MRI was normal; standard EEGs showed anterior epileptiform activity with one-sided predominance, correlating to some ictal clinical features; intellectual and behavioral problems increased with age and disease course. VEEG as a part of presurgical evaluation was considered because of drug-resistant epilepsy. Results All three patients presented an electroclinical pattern consistent with frontal epilepsy. They also had subclinical or “subtle” clinical episodes, both awake and in sleep, corresponding to nonconvulsive status epilepticus (NCSE). The epilepsy started earlier (age 3 years) in the youngest patient with more severe epilepsy. The seizures started later (age 7 and 9 years, respectively) and were rarer in the older patients, who also showed mild cognitive and behavioral disability. Due to the particular electroclinical picture R20 was suspected and cytogenetic analysis was performed. It revealed R20 mosaic karyotype, at 10%, 25% and 40%, respectively. Conclusion The presented cases show again that the diagnosis of R20 syndrome is usually delayed and is based on the very helpful and characteristic for the syndrome electroclinical NCSE pattern and the overall “frontal” seizure appearance. Our cases add further evidence for the genotype-phenotype correlation in the syndrome, since the degree of mosaicism reflects the age of epilepsy onset, the severity and refractoriness of the seizures, and the severity of the associated intellectual and behavioral disabilities.