Question:medium
Phenylketonuria is due to deficiency of:
Phenylketonuria is due to deficiency of:
Updated On: Jun 24, 2026
- Phenylalanine
- Phenylalanine hydroxylase
- Phenylene
- All of these
Show Solution
The Correct Option is B
Solution and Explanation
Step 1: PKU is a single-enzyme metabolic block inherited in an autosomal recessive manner, so we must name the missing enzyme.
Step 2: The defective enzyme is phenylalanine hydroxylase, encoded on chromosome 12 (12q22-q24.1), where more than 400 disease-causing mutations have been described.
Step 3: Without functional PAH, phenylalanine cannot be turned into tyrosine, so it accumulates and overflows into the phenylketone pathway, producing phenylpyruvate detectable in urine.
Step 4: Phenylalanine is the substrate that rises, not the deficiency, and "phenylene" is not a metabolic player, so the deficiency is of phenylalanine hydroxylase.
\[\boxed{\text{Phenylalanine hydroxylase (PAH)}}\]
Step 2: The defective enzyme is phenylalanine hydroxylase, encoded on chromosome 12 (12q22-q24.1), where more than 400 disease-causing mutations have been described.
Step 3: Without functional PAH, phenylalanine cannot be turned into tyrosine, so it accumulates and overflows into the phenylketone pathway, producing phenylpyruvate detectable in urine.
Step 4: Phenylalanine is the substrate that rises, not the deficiency, and "phenylene" is not a metabolic player, so the deficiency is of phenylalanine hydroxylase.
\[\boxed{\text{Phenylalanine hydroxylase (PAH)}}\]
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