Abstracts

Rationale: To clarify characteristics of epilepsy associated with inverted duplication of chromosome 15 (inv dup[15]), we studied epilepsy in eight patients with inv dup (15). Inv dup (15) is the most common supernumerary marker chromosome in humans. Patients with inv dup (15) often have mental retardation, epilepsy (50%) and behavioral problems. However characteristics of epilepsy are still unclear because the occurrence of this disorder is rare. Methods: Eight patients from six hospitals in Japan were included in this study. We retrospectively investigated clinical information, neuroimaging, and interitcal EEG findings. Ictal video EEG was also investigated in four patients. Duplicated regions of inv dup (15) were determined by G-banding, high resolution chromosome analyses or FISH. Results: Epilepsy started with partial seizures in 3 (group P) and generalized seizures in 5 patients (group G). In group P, epilepsy onset age was 112±10months. All patients had larger duplication (q13). Their seizure types did not change evolutionally. Currently, only one patient presents refractory seizures. Interictal EEG showed both bilateral or diffuse (poly) spike and wave bursts and focal discharges, which were considered to be characteristic for inv dup (15). In group G, epilepsy onset age was 26±22 months. Duplication size was larger (q13) in four patients and smaller (q11) in one. Epilepsy started with atypical absence which was later replaced by tonic seizures in one, and with epileptic spasms in the other four patients. Epileptic spasms were easily controlled in only one patient and replaced by tonic seizures in two patients or partial seizures in one. Interictal EEG showed hypsarrythmia in one and generalized discharges in the others. Conclusions: Our data suggested that inv dup (15) showed two different characteristic epileptic phenotypes. The first type is childhood onset partial epilepsy with interictal bilateral (poly) spike and waves. The second type is infantile or early childhood onset generalized epilepsy with epileptic spasms. When epileptic children of unknown origin showed above-mentioned characteristics, we should consider possibility of inv dup (15). In this study, duplication size was smaller in one who had refractory seizures. Only four of seven patients with large inv dup (15) presented refractory seizures. Our study showed the discrepancy between the genotype and phenotype, though several studies reported the genotype-phenotype correlation existed in inv dup (15).