A comatose infant is brought to the ER. In the course of the examination, plasma

Question

A comatose infant is brought to the ER. In the course of the examination, plasma ammonia was found to be elevated 20-fold over normal values. Urine orotic acid and uracil, that require carbamoyl phosphate for their formation, were both greater than normal. A defect of which of the following enzymes is the most likely diagnosis?

A. Arginase

B. Argininosuccinate lyase

C. Carbamoyl phosphate synthetase 1 (ammonia substrate)

D. Carbamoyl phosphate synthetase 2 (glutamine substrate)

E. Ornithine transcarbamoylase

Explanation / Answer

Answer: (A) Arginase

Description:Argininemia also called arginase deficiency is an autosomal recessive urea cycle disorder where a deficiency of the enzyme arginase causesThe symptoms of all urea cycle disorders vary in severity from the excessive accumulation of ammonia in the blood and body tissues-hyperammonemia.Common symptoms include lack of appetite, vomiting, drowsiness, seizures and coma.Arginase deficiency is an inherited disorder that causes the amino acid arginine and ammonia to accumulate gradually in the blood. Ammonia, which is formed when proteins are broken down in the body.

Urinary uracil excretion was normal in patients with arginase deficiency but Uridine and orotic acid, not normally detected, were excreted in large amounts and were directly influenced by protein intake and excretions correlated with urinary arginine excretion.

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