As the degree of ID does not appear to correlate with the severity of the seizures and/or the age of onset of epilepsy, STXBP1-EE is not thought to be a simple Early Onset Epileptic Encephalopaty-EOEE, but a more complex neurodevelopmental disorder (DEE, Developmental and Epileptic Encephalopaty), where both ID (often occurring before the onset of epilepsy) and epilepsy play a synergic role in the phenotype evolution [25,26,27]. The gene discussed is STXBP1; the disease is neurodevelopmental disorder.