XEN496 (Ezogabine) in Children With KCNQ2 Developmental and Epileptic Encephalopathy

Inclusion Criteria: * Male or female subjects aged from 1 month to less than 6 years, with a body weight of ≥3.0 kg at screening. * Documented evidence of a genetic test result from an appropriately accredited laboratory, consistent with a diagnosis of KCNQ2-DEE (pathogenic, likely pathogenic, variant of unknown significance, or inconclusive but unlikely to support an alternate diagnosis). * Seizure onset within 2 weeks after birth and EEG and documented clinical history consistent with KCNQ2-DEE. * Magnetic resonance imaging has been performed and is without evidence of structural abnormalities, including but not limited to, hypoxia, hypoxia-ischemia, ischemia (arterial or venous), stroke, sinovenous thrombosis, intracranial hemorrhage, or focal or global brain malformation. Brain MRI changes that are described as being associated with the KCNQ2-DEE and presumed to be secondary to the disease itself, will not be exclusionary. * Must have had focal tonic or other countable motor seizures in the 28 days prior to screening. * Taking 1 and no more than 4 concomitant antiseizure medications (ASMs). All doses must be stable for at least 1 week prior to screening and expected to be maintained throughout the duration of the study. * Vagal nerve stimulation (VNS) is allowed and will not be counted as a concomitant ASM. The VNS device must be implanted for at least 6 months before screening, and the device settings must be stable for at least 6 weeks prior to screening and throughout…