A 7-month-old infant presents with history of vomiting & failure to thrive. Patient improved with IV glucose. After one month, returns with same complaints. On evaluation, found to have high glutamine and uracil. Which is the likely enzyme defect?: (A) CPS1, (B) Ornithine transcarbamylase, (C) Arginase, (D) Arginosuccinase lyase
Answer is B. b. Ornithine transcarbamylase(Ref: Nelson Textbook of Pediatrics, 19/e p447-450; Nelson's 20/e p 669-674)Discussing about the findings of each of the above enzyme deficiencies, one by one.a. CPS1* Hyperammonemia with markedly increased glutamine and alanine* Urinary orotic acid is usually low or may be absentb. Ornithine transcar-bamylase* Hyperammonemia with elevated plasma glutamine and alanine* Hyperammonemia with elevated plasma glutamine and alanine)c. Arginase* Marked elevations of arginine in plasma and CSF* Urinary excretion of orotic acid, arginine, lysine, cystine, & ornithine are increasedd. Arginosuccinase lyase* Increase in plasma argininosuccinic acid, citrulline glutamine and alanine* Argininosuccinic acid is found in large amounts in urine and spinal fluid* Note: Orotic acid, (elevated in OTC deficiency) converts to Uracil via Pyrimidine pathway.