ROSH Gastrointestinal Practice Exam

A child with a musty smelling urine and developmental delays might be suspected to have a deficiency of which amino acid?

1. Tyrosine

2. Leucine

3. Phenylalanine

4. Asparagine

The correct answer is: Phenylalanine

A child presenting with musty smelling urine and developmental delays raises suspicion for phenylketonuria (PKU), a condition caused by a deficiency in the enzyme responsible for the metabolism of phenylalanine, an amino acid. In PKU, the accumulation of phenylalanine leads to not only the characteristic odor in urine but also significant neurological impairment and developmental delays if left untreated. The musty odor, often described as similar to that of musty or moldy substances, is specifically attributed to the buildup of phenylalanine and its metabolites. In contrast, tyrosine, leucine, and asparagine are associated with different metabolic disorders or dietary considerations but do not cause the specific symptoms of musty-smelling urine along with developmental delays. For instance, tyrosine is often involved in conditions such as tyrosinemia, which manifests differently. Leucine is linked to maple syrup urine disease but does not typically present with a musty smell. Asparagine does not have the same clinical implications in terms of odor and developmental issues. Thus, the biochemical marker of musty smelling urine alongside developmental delays distinctly points to a phenylalanine deficiency linked to PKU.