Which condition is characterized by a "mousy" odor in urine?

• A. Tyrosinemia
• B. Phenylketonuria
• C. Homocystinuria
• D. Cystinuria

Answer: (B)

Phenylketonuria (PKU) is characterized by a "mousy" or musty odor in urine due to the accumulation of phenylalanine and its metabolites. In PKU, the body lacks the enzyme phenylalanine hydroxylase, which is needed to convert phenylalanine into tyrosine. As a result, phenylalanine and its byproducts build up in the body, leading to various health issues, including intellectual disabilities if not managed through dietary restrictions.

The distinctive odor of urine in patients with PKU is often noticed from infancy and is one of the key indicators used in newborn screening programs to detect the condition early. The presence of this characteristic odor serves as a diagnostic clue that contributes to the overall clinical picture of phenylketonuria.

In contrast, tyrosinemia may result in different metabolites in urine but does not typically produce a mousy odor. Similarly, homocystinuria and cystinuria are associated with other odors and metabolic disturbances that do not match the specific mousy characteristic. Each of these conditions presents with distinct biochemical and clinical features, which includes the type of odors associated with the urine.