Uridine monophosphate (UMP)-responsive developmental and epileptic encephalopathy: A case report of two siblings and a review of literature.

Developmental and epileptic encephalopathy type 50 is an autosomal recessive disorder caused by pathogenic variants in . This gene encodes a multifunctional enzyme involved in the initial steps of pyrimidine synthesis. Uridine treatment has been shown to be effective in this disease. Here, we report two siblings with 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.