Inherited hyperammonemia is a result of deficiency of which enzyme of Krebs-Henseleit urea cycle?
**Core Concept**
The Krebs-Henseleit urea cycle is a crucial metabolic pathway that converts ammonia into urea for excretion. A deficiency in any of the enzymes involved in this cycle can lead to inherited hyperammonemia, a potentially life-threatening condition.
**Why the Correct Answer is Right**
The correct answer is a deficiency in the enzyme carbamoyl phosphate synthetase I (CPS I). CPS I is responsible for the first committed step of the urea cycle, where ammonia is converted into carbamoyl phosphate. This reaction is crucial for the detoxification of ammonia. A deficiency in CPS I leads to a buildup of ammonia in the body, resulting in hyperammonemia.
**Why Each Wrong Option is Incorrect**
**Option A:** Ornithine transcarbamylase (OTC) deficiency leads to hyperammonemia, but it is not the correct answer. OTC deficiency is a different enzyme deficiency that affects the urea cycle.
**Option B:** Argininosuccinate synthetase deficiency leads to citrullinemia, not hyperammonemia. While it is a urea cycle disorder, it is not the correct answer.
**Option C:** Arginase deficiency leads to arginemia, not hyperammonemia. It is a different urea cycle disorder that affects the conversion of arginine to urea.
**Option D:** This option is missing.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that inherited hyperammonemia can present with a range of symptoms, from mild to severe, and can be life-threatening if not promptly treated. The diagnosis often involves a combination of clinical presentation, laboratory tests, and genetic analysis.
**Correct Answer: D. Carbamoyl phosphate synthetase I.**