An individual harboring a mutation in OTC would be expected to exhibit which of the following measurable abnormalities?
A) citrullinemia
B) elevated urinary excretion of argininosuccinic acid
C) elevation in blood orotic acid
D) excess production of foam cells
E) uric acid deposition in the joints

Question

Quizplus · Accepted Answer

A mutation in the OTC (ornithine transcarbamylase) gene leads to an accumulation of carbamoyl phosphate, which is then converted to orotic acid, resulting in elevated blood orotic acid levels.  A deficiency in OTC results in one of the urea cycle defect diseases, which are the major causes of hyperammonemia in the newborn. Differentiation of which urea cycle enzyme is defective and causing the hyperammonemia can be accomplished by analysis of the levels of the various intermediates in the cycle (see Figure 29-9). Since a defect in OTC prevents incorporation of carbamoyl phosphate into ornithine, the carbamoylphosphate will leave the mitochondria and serve as a precursor for the synthesis of the pyrimidine nucleotides in excess of the need, leading to an elevation of orotic acid (pyrimidine intermediate) in the blood.

An Individual Harboring a Mutation in OTC Would Be Expected