Refining the electroclinical phenotype of 15q11.2 microdeletion: EEG biomarker overlap with Angelman syndrome

The 15q11.2 microdeletion is a chromosomal condition associated with a broad epileptic phenotype. It is differentiated from Angelman syndrome, which is typically a larger maternal deletion in an overlapping area. We describe a patient with a 15q11.2 microdeletion that has clinical and EEG biomarker features similar to those seen in Angelman syndrome. The patient was found to have a maternally inherited, likely pathogenic 258 kb deletion at 15q11.2. Novel electroclinical features associated with this finding included myoclonic absence seizures and other EEG findings consistent with the syndrome of Epilepsy with Myoclonic absences. The 15q11.2 microdeletion syndrome has a broad phenotype, and accuracy of diagnosis appears variable and inconsistent. EEG and knowledge of unique biomarkers may be a tool that can further refine genetic diagnosis.