A 2-year-old child presents with fair skin, blue eyes, musty body odor, intellectual disability, and seizures. Urine ferric chloride test gives a green color. Which metabolite is responsible for the musty odor?
- A Phenylpyruvate
- B Phenylacetate ✓
- C Homogentisic acid
- D Methylmalonic acid
Correct answer: B. Phenylacetate
Explanation
In classic PKU, accumulation of phenylalanine leads to alternative transamination to phenylpyruvate (a phenylketone, detected by ferric chloride as green), which is further decarboxylated to phenylacetate and reduced to phenyllactate. Phenylacetate is the volatile compound responsible for the characteristic musty or mousy odor in untreated PKU patients. The intellectual disability results from high phenylalanine competing with other large neutral amino acids at the blood-brain barrier, impairing neurotransmitter synthesis.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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