Abstract
Developmental and epileptic encephalopathy type 50 is an autosomal recessive disorder caused by pathogenic variants in CAD. This gene encodes a multifunctional enzyme involved in the initial steps of de novo pyrimidine synthesis. Uridine treatment has been shown to be effective in this disease. Here, we report two siblings with CAD pathogenic variants who presented with developmental regression and intractable epilepsy. Treatment with oral uridine monophosphate (UMP) resulted in remarkable and rapid clinical improvement in terms of developmental progress and seizure control. We also reviewed previous literature and summarized all reported patients to date.