Developmental epileptic encephalopathies (DEEs) are severe childhood conditions that cause early-onset seizures and developmental delay. Although genetic testing can identify a cause in many patients, some remain undiagnosed despite extensive investigations. In this study, we used a newer method called optical genome mapping (OGM), which can detect certain genetic changes missed by standard tests. Among 32 children with DEE who remained undiagnosed despite multiple genetic tests, this approach identified underlying causes in two patients. These findings show that OGM can complement existing genetic tests and help provide answers for families still searching for a diagnosis. (https://jmg.bmj.com/content/early/2026/04/16/jmg-2026-111485)