You’re doing a Q-bank set and a “bleeding gums + poor wound healing” vignette pops up. Easy, right—scurvy. But the real points aren’t in naming vitamin C deficiency; they’re in why collagen fails, what step is disrupted, and how to eliminate every distractor that sounds collagen-adjacent. Let’s break it down the way the exam writes it: one correct mechanism, several tempting traps.
The Vignette (Classic Q-bank Style)
A 62-year-old man with alcohol use disorder and a diet mostly consisting of tea and toast presents with fatigue, gum bleeding, easy bruising, and “small bumps” around hair follicles on his legs. He has poor wound healing after a minor cut. Exam shows perifollicular hemorrhages and corkscrew hairs.
Question: The patient’s symptoms are primarily due to impaired function of which process?
The Correct Answer: Impaired Hydroxylation of Proline and Lysine in Collagen
Scurvy (vitamin C deficiency) impairs hydroxylation of proline and lysine residues in the rough ER during collagen synthesis.
Why vitamin C matters
Vitamin C (ascorbic acid) is a required cofactor for prolyl hydroxylase and lysyl hydroxylase, which use Fe²⁺. Vitamin C helps maintain iron in the reduced (Fe²⁺) state so these enzymes can function.
What goes wrong in collagen
Without hydroxylation:
- The collagen triple helix becomes unstable
- Collagen has decreased tensile strength
- Blood vessels and connective tissue become fragile
Clinical consequences (tie directly to symptoms)
High-yield scurvy findings:
- Bleeding gums
- Easy bruising / ecchymoses
- Perifollicular hemorrhage
- Corkscrew hairs
- Poor wound healing
- Anemia (can be multifactorial: bleeding + impaired iron absorption)
Collagen Synthesis: Where the Defect Lives (Step-by-Step)
Here’s the big picture—USMLE loves asking you to locate the defect by cellular location and enzyme.
| Step | Location | Key event | High-yield notes |
|---|---|---|---|
| Translation of pro-α chains | RER | Synthesis of collagen precursors | Gly-X-Y repeats (often proline/lysine) |
| Hydroxylation of proline/lysine | RER | Requires vitamin C | Scurvy → unstable triple helix |
| Glycosylation | RER | Add glucose/galactose to hydroxylysine | Not vitamin C–dependent |
| Triple helix formation (procollagen) | RER | 3 chains coil | |
| Secretion | Golgi → extracellular | Procollagen exported | |
| Cleavage of propeptides → tropocollagen | Extracellular | Procollagen peptidase | Defect → certain EDS types |
| Cross-linking | Extracellular | Lysyl oxidase forms cross-links | Requires copper (Cu²⁺) |
Scurvy = hydroxylation problem in the RER.
Why Each Distractor Matters (and How to Kill It Fast)
Below are common answer choices that show up in scurvy/collagen questions. The key is to map each to the correct deficiency/disease and the specific collagen step.
Distractor 1: “Decreased activity of lysyl oxidase”
Why it’s tempting: It’s collagen-related and causes weak connective tissue.
Why it’s wrong for scurvy: Lysyl oxidase is copper-dependent, not vitamin C–dependent, and acts extracellularly to cross-link collagen.
What it actually points to:
- Copper deficiency (e.g., malnutrition, bariatric surgery, Menkes disease)
- Findings: connective tissue weakness, poor wound healing can happen, but scurvy’s perifollicular hemorrhages/corkscrew hairs/gum bleeding are classic for vitamin C.
Board tip:
- Vitamin C → hydroxylation (RER)
- Copper → cross-linking (extracellular)
Distractor 2: “Defective cleavage of procollagen to tropocollagen”
Why it’s tempting: Sounds like a maturation step and can cause fragile tissues.
Why it’s wrong: That’s a problem with procollagen peptidase (extracellular processing), not vitamin C.
What it actually points to:
- Ehlers-Danlos syndrome (EDS) (certain types)
- Findings: hyperextensible skin, hypermobile joints, easy bruising, poor wound healing, tissue fragility
Board tip: If the stem emphasizes joint hypermobility + stretchy skin, think EDS, not scurvy.
Distractor 3: “Decreased synthesis of type I collagen”
Why it’s tempting: Type I collagen is the major structural collagen—bones, skin, tendons. Weak type I sounds like bleeding and poor healing.
Why it’s wrong: Scurvy is not a failure to synthesize collagen chains; it’s a post-translational modification defect (hydroxylation). The pro-α chains are made, but the triple helix is unstable.
What it actually points to:
- Osteogenesis imperfecta (usually COL1A1/COL1A2 mutation)
- Findings: fractures with minimal trauma, blue sclerae, hearing loss, dentinogenesis imperfecta
Board tip:
- Scurvy = “collagen made poorly” (unstable)
- OI = “collagen made wrong/insufficient” (type I defect)
Distractor 4: “Impaired gamma-carboxylation of glutamate residues”
Why it’s tempting: Bleeding gums/bruising → must be a coagulation issue.
Why it’s wrong: That mechanism is vitamin K deficiency/warfarin, affecting clotting factors—not collagen.
What it actually points to:
- Decreased activation of factors II, VII, IX, X, proteins C and S
- Prolonged PT first (factor VII has shortest half-life), bleeding tendency
How to separate from scurvy quickly:
- Scurvy: perifollicular hemorrhages, corkscrew hairs, gum bleeding + poor wound healing
- Vitamin K issue: abnormal coag labs, bleeding without hair/follicle findings
Distractor 5: “Defective formation of fibrillin microfibrils”
Why it’s tempting: Connective tissue disorder with vascular fragility vibe.
Why it’s wrong: That’s Marfan syndrome, which is not collagen hydroxylation.
What it actually points to:
- FBN1 mutation → abnormal fibrillin-1
- Findings: tall habitus, arachnodactyly, lens subluxation (up), aortic root dilation
Distractor 6: “Decreased hydroxylation due to impaired copper absorption”
Why it’s tempting: Mixes up copper and hydroxylation, hoping you’ll match “cofactor problem.”
Why it’s wrong: Copper is for lysyl oxidase (cross-linking), not hydroxylation. Hydroxylation needs vitamin C and Fe²⁺.
High-Yield “One-Liners” You Want in Your Head
- Scurvy: defective hydroxylation of proline and lysine in collagen → unstable triple helix → bleeding gums, perifollicular hemorrhage, corkscrew hairs, poor wound healing.
- Vitamin C keeps iron in Fe²⁺ for prolyl/lysyl hydroxylases.
- Copper (lysyl oxidase) = collagen cross-linking (extracellular).
- EDS = defective collagen processing/structure → hypermobile joints, hyperextensible skin.
- OI = defective type I collagen → fractures, blue sclerae, hearing loss.
- Vitamin K = gamma-carboxylation of clotting factors (II, VII, IX, X, C, S)—coagulation problem, not collagen.
Mini Self-Check (What the Exam Really Asked)
If the question asks why bleeding + poor wound healing happen, the best mechanism is usually:
↓ hydroxylation of proline/lysine in collagen due to vitamin C deficiency → unstable collagen triple helix
That’s the mechanism that unifies vessel fragility, skin findings, and impaired wound repair.
Rapid-Fire Table: Collagen-Adjacent Defects You Must Differentiate
| Condition | Defect | Key clue(s) |
|---|---|---|
| Scurvy | ↓ hydroxylation (Vit C) | Bleeding gums, perifollicular hemorrhage, corkscrew hairs |
| Copper deficiency / Menkes | ↓ cross-linking (lysyl oxidase) | Connective tissue weakness + neuro findings in Menkes (kinky hair) |
| EDS | Collagen processing/structure defects | Hypermobile joints, hyperextensible skin |
| OI | Type I collagen synthesis defect | Multiple fractures, blue sclerae, hearing loss |
| Marfan | Fibrillin-1 defect | Aortic root dilation, lens up, tall habitus |
| Vit K deficiency/warfarin | ↓ gamma-carboxylation | Abnormal PT/INR, bleeding without scurvy hair/follicle signs |
Wrap-Up: The “Answer Choice Strategy” That Scores Points
When you see a collagen vignette, don’t just pattern-match the diagnosis—map the symptom cluster to the collagen step:
- Scurvy screams RER hydroxylation failure
- Copper screams extracellular cross-linking failure
- EDS/OI scream inherited structural problems
- Vitamin K screams coagulation, not connective tissue
That’s how you turn a “gimme” question into guaranteed points.