Orotic aciduria is a rare (fewer than 20 reported cases) inborn error of metabolism.
Affected individuals exhibit retarded growth and development, as well as a megaloblastic anemia.
The disease, which is autosomal recessive, is caused by a deficiency of the UMP synthase complex (phosphoribosyltransferase and orotate decarboxylase) in the pyrimidine biosynthetic pathway (Table 14- 2).
The gene for UMP synthase is on the long arm of chromosome 3 (Table 16-5).
Affected individuals excrete about 1.5 g of orotate daily; this is 1000 times the normal value.
The anemia is due to a deficiency of nucleotides, precursors of DNA and RNA, in rapidly dividing bone marrow cells.
Oral pyrimidines (synthetic or from yeast extract) provide substrates for pyrimidine nucleotide, RNA, and DNA synthesis to correct the anemia of orotic aciduria.