Uridine monophosphate synthase (UMPS) is the enzyme responsible for converting orotic acid to uridine monophosphate (UMP), which is an essential component of pyrimidine nucleotides. This enzyme actually has two enzymatic functions: orotic phosphoribosyltransferase (OPRTase) and orotidine monophosphate decarboxylase (OMPDCase), corresponding to the last two steps in pyrimidine synthesis. Since pyrimidines are vital ingredients of nucleic acids, it follows that a deficiency of UMPS can have quite severe consequences.

This disorder is of particular interest in Holstein cattle, because it is one of the few cases in which an embryonic lethal has been identified. To date, the only known cause of this disorder in cattle is a mutation in the UMPS gene, resulting in a complete deficiency of functional UMPS.It is not surprising that affected embryos result in embryonic death around 40 days in utero. The practical effect of this disorder is that carrier cows show a higher rate of return to service, because some of their pregnancies end in early natural abortion.