Enzyme deficiency
OTC deficiency
What is missing: Ornithine transcarbamoylase.
Why the signs follow
The most common urea cycle disorder and the only X-linked one. Carbamoyl phosphate backs up out of the mitochondrion into pyrimidine synthesis, producing orotic aciduria, but with no megaloblastic anemia, which separates it from orotic aciduria proper.
Written for exam preparation, not for diagnosis.