A patient with a rare urea cycle disorder will most likely have which of the following issues?

A patient with a rare urea cycle disorder typically experiences elevated ammonia levels due to the inability of the body to properly convert ammonia into urea for excretion. The urea cycle is a series of biochemical reactions that occur in the liver, primarily responsible for detoxifying ammonia derived from the breakdown of proteins. When there is a defect in any of the enzymes associated with this cycle, ammonia accumulates in the bloodstream because it cannot be efficiently converted to urea.

Elevated ammonia levels can lead to toxic effects, particularly on the central nervous system, resulting in symptoms such as confusion, lethargy, or, in severe cases, coma. This highlights the importance of the urea cycle and its role in maintaining nitrogen balance in the body.

In contrast, other choices relate to different metabolic issues. Decreased energy metabolism may occur in various metabolic disorders but is not as directly associated with urea cycle disorders specifically. Reduced muscle mass can be a consequence of multiple conditions but is not a primary issue with urea cycle disorders. Lastly, high creatinine levels are generally associated with renal function impairment rather than specifically linked to urea cycle dysfunction. Therefore, the most direct and relevant consequence of a urea cycle disorder is the elevation of ammonia levels.