A two-day-old neonate presents with hyperammonemia, lethargy, poor feeding, and seizures. Urine analysis reveals elevated levels of orotic acid. A deficiency in which of the following enzymes is the most likely diagnosis?

✓ Correct Answer: Option B

Ornithine transcarbamylase (OTC) deficiency is an X-linked urea cycle disorder. Carbamoyl phosphate accumulates and is shunted to pyrimidine synthesis, leading to elevated orotic acid. This, combined with hyperammonemia, confirms the diagnosis.