Question:medium
A child presents with gum bleeding, perifollicular hemorrhages, petechiae, and recurrent fractures. Which enzyme deficiency is most likely?
A child presents with gum bleeding, perifollicular hemorrhages, petechiae, and recurrent fractures. Which enzyme deficiency is most likely?
Show Hint
Vitamin C deficiency impairs collagen synthesis by reducing hydroxylation of proline and lysine.
Updated On: May 14, 2026
- Lysyl oxidase
- Prolyl hydroxylase
- Tyrosinase
- Alkaline phosphatase
Show Solution
The Correct Option is B
Solution and Explanation
Step 1: Understanding the Question:
The clinical features (bleeding gums, petechiae, perifollicular hemorrhages) are the hallmark signs of Scurvy, which is caused by Vitamin C (ascorbic acid) deficiency.
We need to identify the enzyme that is functionally impaired due to the lack of Vitamin C.
Step 2: Detailed Explanation:
Vitamin C Function: Vitamin C acts as a mandatory reducing agent (cofactor) to maintain the iron atom of certain hydroxylase enzymes in its active ferrous (Fe2+) state.
Critical Enzymes: The two primary enzymes affected are Prolyl hydroxylase and Lysyl hydroxylase.
Role in Collagen Synthesis: These enzymes are responsible for hydroxylating proline and lysine residues on the pre-pro-collagen chains within the endoplasmic reticulum.
- Hydroxyproline is essential for the formation of stable hydrogen bonds that hold the collagen triple helix together.
Pathophysiology of Scurvy: Without Vitamin C, Prolyl hydroxylase becomes inactive. The resulting collagen is structurally weak and unstable, leading to blood vessel fragility (hemorrhages) and poor bone matrix formation (fractures).
Evaluating other options:
Lysyl oxidase (A): Required for collagen cross-linking; requires Copper, not Vitamin C.
Tyrosinase (C): Involved in melanin production; deficiency causes albinism.
Alkaline phosphatase (D): Involved in mineralization, not the initial collagen structure.
Step 3: Final Answer:
The symptoms of scurvy result directly from the failure of Prolyl hydroxylase to stabilize the collagen triple helix in the absence of Vitamin C.
The clinical features (bleeding gums, petechiae, perifollicular hemorrhages) are the hallmark signs of Scurvy, which is caused by Vitamin C (ascorbic acid) deficiency.
We need to identify the enzyme that is functionally impaired due to the lack of Vitamin C.
Step 2: Detailed Explanation:
Vitamin C Function: Vitamin C acts as a mandatory reducing agent (cofactor) to maintain the iron atom of certain hydroxylase enzymes in its active ferrous (Fe2+) state.
Critical Enzymes: The two primary enzymes affected are Prolyl hydroxylase and Lysyl hydroxylase.
Role in Collagen Synthesis: These enzymes are responsible for hydroxylating proline and lysine residues on the pre-pro-collagen chains within the endoplasmic reticulum.
- Hydroxyproline is essential for the formation of stable hydrogen bonds that hold the collagen triple helix together.
Pathophysiology of Scurvy: Without Vitamin C, Prolyl hydroxylase becomes inactive. The resulting collagen is structurally weak and unstable, leading to blood vessel fragility (hemorrhages) and poor bone matrix formation (fractures).
Evaluating other options:
Lysyl oxidase (A): Required for collagen cross-linking; requires Copper, not Vitamin C.
Tyrosinase (C): Involved in melanin production; deficiency causes albinism.
Alkaline phosphatase (D): Involved in mineralization, not the initial collagen structure.
Step 3: Final Answer:
The symptoms of scurvy result directly from the failure of Prolyl hydroxylase to stabilize the collagen triple helix in the absence of Vitamin C.
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