Abstracts

Rationale: Children with the inv dup (15) or idic (15) syndrome (tetrasomy 15q) often present with early hypotonia, developmental delay/intellectual disability, autistic behavior and epilepsy. There are limited reports regarding the seizure and EEG features of patients with this syndrome. The purpose of this study is to describe the electroclinical features of epilepsy in a series of children with idic(15) followed at one centre.Methods: Patients were identified from the Neurogenetic, Epilepsy and Diagnostic Neurophysiology databases. The medical records, EEG, neuroimaging and genetic testing were reviewed. Seizure types were classified according to the ILAE Revised Classification and Terminology (Epilepsia 2010).Results: 9 patients were identified, 5 males; 4 females). At most recent follow-up, the mean age was 7 years (range 2.7 to 14.8 years). 7 patients developed epilepsy, at a mean age of 1.4 years (range 13 hours to 6.5 years). One male without epilepsy is mosaic for idic(15). Five children had epileptic encephalopathy. Seizures were documented during video-EEG recordings in 5 patients. The most common seizure type was epileptic spasms n=4 with an electrodecremental pattern on EEG. Tonic seizures were recorded in 3 patients with an electrodecremental or incremental pattern. Focal seizures were recorded in 3 patients with a focal evolving EEG pattern. Myoclonic seizures were seen in one patient with generalized polyspikes, atonic seizures (n=1) and atypical absence (n=1) both with generalized atypical spike and wave. One patient had resolution of epileptic spasms with Vigabatrin but subsequently developed other seizure types. Patients received a mean of 5 (1-10) anti-seizure medications and 2 were treated with the ketogenic diet. At most recent follow-up, one child was seizure free longer than 1 year but the interictal EEG demonstrated multifocal slowing and spikes. Six children had treatment resistant epilepsy. All patients had moderate/severe intellectual impairment and 6 had autism. MR imaging was normal in 8 patients, nodular heterotopia was seen in one patient.Conclusions: Epilepsy and epileptic encephalopathy are common in children with isodicentric chromosome 15 abnormality. Epileptic spasms and tonic seizures are the most common seizure types. The ictal recordings in this case series expands the electroclinical phenotype of isodicentric chromosome 15 and highlights the importance of genetic testing including chromosome microarray in in children with treatment resistant epilepsy and developmental delay.