Megaloblastic anemia with anisocytosis and
hypochromia appearing a few weeks or months after birth is the first
manifestation. It does not respond to iron, folic acid, or vitamin B12.
If the disorder is unrecognized, failure to thrive with growth and
developmental retardation ensues. Urinary obstruction (renal, ureteral, or
urethral) from orotic acid crystals has been reported. For treatment, the
enzymatic defect can be bypassed by the administration of uridine, which is
converted into uridine monophosphate by uridine kinase. The hematologic
response is quick. The dosage is adapted in order to achieve the lowest
possible urinary output of orotic acid.