Which metabolic disorder is indicated by a rancid smell in urine?

The rancid smell in urine is most notably associated with tyrosinemia, a metabolic disorder characterized by the accumulation of tyrosine and its byproducts due to a deficiency in the enzyme responsible for its metabolism. The disorder leads to the production of unusual metabolites, which can result in distinctive odors, including a rancid smell that resembles that of rotting vegetables or rancid butter.

In tyrosinemia, the body is unable to properly break down tyrosine, resulting in an increase in harmful substances like fumarate and malate. This disruption in normal metabolism leads to the characteristic odor linked with the condition. Spotting this trait can aid clinicians in narrowing down potential metabolic disorders when analyzing urine samples.

While diabetes mellitus, maple syrup urine disease, and phenylketonuria each have their unique urine odors—such as a sweet odor in diabetes or a maple syrup smell in maple syrup urine disease—they do not produce the rancid smell associated specifically with tyrosinemia. Thus, the identification of a rancid smell in urine directs attention to tyrosinemia as the likely cause.