UMPS and orotic aciduria: Uridine supplementation has been successfully implemented for rare disorders such as orotic aciduria and carbamoyl phosphate synthetase II, aspartate transcarbamylase and dihydroorotase (CAD) deficiency, which are disorders in which enzymes responsible for pyrimidine biosynthesis, such as uridine monophosphate synthetase (UMPS) or CAD, are mutated; thus, uridine provides alternative precursors for pyrimidine synthesis42,43.