Hereditary orotic aciduria

A rare autosomal recessive disorder characterized by retarded growth, anemia and excessive urinary excretion of orotic acid. It is due to a severe deficiency in the activity of the pyrimidine pathway enzyme uridine 5'-monophosphate (UMP) synthase (bifunctional enzyme containing two activities: orotate phosphoribosyltransferase and orotidine 5'-monophosphate decarboxylase), coded by a single gene (UMPS) localized to chromosome 3q13.