Operational definition of developmental and epileptic encephalopathies to underpin the design of therapeutic trials

Developmental and epileptic encephalopathies (DEEs) are the most severe group of epilepsies, characterized by drug-resistant seizures and developmental slowing or regression. DEEs encompass many epilepsy syndromes, although not all patients with a DEE can be classified into a specific syndrome. Our understanding of the etiologies of DEEs has been revolutionized with next-generation sequencing, with more than 900 genes implicated, in addition to structural causes. It is therefore now possible to consider precision medicine and novel therapeutic approaches for these devastating diseases with trials of repurposed and new drugs, including gene therapies. Trials are being designed to target either DEE diseases more broadly, specific DEE syndromes, or specific genetic DEEs. To serve this purpose, a clear operational definition of DEEs is needed to ensure that appropriate patients are selected for trials with precisely defined, targeted outcome measures. Herein we propose the operational definition of DEEs to set the stage for the development of DEE therapies.