Wednesday, February 13, 2019

Orotic aciduria

Hello Awesomites!
The question has helped me to learn the pyrimidine biosynthesis and urea cycle better. Felt like sharing it.
Let's get started.

OROTIC ACIDURIA= Excessive excretion of orotic acid in urine.
Orotic aciduria is caused by defect in either UMP synthase enzyme or Ornithine trancarbomylase (OTC) enzyme.

When UMP synthase is defective, orotic acid builds up and the synthesis of nucleic acid is impaired, leading to deficient hematopoiesis and growth. Orotic aciduria is associated with megaloblastic anemia due to decreased pyrimidine synthesis. This megaloblastic anemia is refractory to Vitamin B12, folic acid supplementation. This megaloblastic anemia present in infants.

Incessant crying due to orotic acid crystals in ureter produces colicky pain
Growth retardation

Tachycardia and faint murmur due to hyperdynamic circulation in anemia.

Urine analysis show orotic acid crystals.
Peripheral blood smear show hypochromic megaloblastic anemia and hypersegmented neutrophils.
We can distinguish this increase in orotic acid secondary to OTC deficiency from hereditary orotic aciduria by looking at blood ammonia levels and the BUN (blood urea nitrogen).

HYPERAMMONAEMIA is present in OTC deficiency.

Administration of uridine, which is converted to UMP, will bypass the metabolic block and provide the body with a source of pyrimidine. Uridine triacetate is a drug approved by FDA to be used in the treatment of hereditary orotic aciduria.

Have a great day.
-Upasana Y. :)

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