Praxis-induced reflex seizures in two Japanese cases with ring chromosome 20 syndrome

Ring chromosome 20 syndrome is an epileptic and neurodevelopmental encephalopathy that occurs in children, characterised by a triad of refractory frontal lobe seizures, recurrent non-convulsive status epilepticus and frontal lobe-dominant paroxysmal discharges. However, details of other clinical features associated with ring chromosome 20 syndrome remain unknown. Here, we report two patients with ring chromosome 20 syndrome who had praxis-induced reflex seizures. Case 1 was an 11-year-old girl who presented with seizures triggered by specific activities such as mental and written calculations, writing, decision-making, recall, sudden changes in routine or ambient temperature and bathing. During calculations, left frontal lobe-dominant, 3-Hz slow-wave bursts were observed on EEG. Lacosamide effectively suppressed her tonic seizures. Case 2 was a six-year-old boy who presented with seizures triggered by specific activities such as calculations, recall and bathing. During calculations, frontal lobe-dominant, 3-Hz spike and slow-wave bursts were observed on EEG. Although his epilepsy was refractory, gabapentin reduced the frequency of focal seizures. In both cases, the hyperexcitability in the frontal lobe may have spread to the motor cortex and precipitated praxis-induced seizures. Therefore, in addition to the known characteristic triad, praxis-induced reflex seizures may also be a feature of ring chromosome 20 syndrome.