WBR0644

Author	[[PageAuthor::Rim Halaby, M.D. [1]]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Biochemistry
Sub Category	SubCategory::Dermatology, SubCategory::General Principles
Prompt	[[Prompt::A 54 year old homeless, alcoholic man with history of multiple hospital admissions presents to the emergency room for 3 hours of increasing shortness of breath. On exam, the patient is afebrile, his pulse is 102 bpm, blood pressure is 143/89 mmHg, and respiratory rate is 24 breaths per minute. The ED physician notices several large bruises on the man's arms, legs, and anterior abdomen. Examination of the oral cavity reveals poor denition with severely swollen gums. The physician also notes 2 ulcers on the man's left sole which were reportedly there the last time the patient was admitted to the hospital 4 months ago. Which of the following steps in collagen synthesis is likely to be defective in this patient? ]]
Answer A	AnswerA::A
Answer A Explanation	AnswerAExp::This step refers to the hydroxylation of proline and lysine residues mediated by Vitamin C. Scurvy would lead to a defect in this phase of collagen synthesis.
Answer B	AnswerB::B
Answer B Explanation	AnswerBExp::This step refers to glycosylation of specific residues in the collagen chain. It is not affected by vitamin C deficiency.
Answer C	AnswerC::C
Answer C Explanation	AnswerCExp::This step refers to collagen triple helix (procollagen) formation. It is defective in osteogenesis imperfecta. It is not affected by vitamin C deficiency.
Answer D	AnswerD::D
Answer D Explanation	AnswerDExp::This step refers to the cleavage of the terminal regions of procollagen. It is not affected by vitamin C deficiency.
Answer E	AnswerE::E
Answer E Explanation	AnswerEExp::This refers to collagen cross-linking via lysyl-oxidase (requires copper). This step is defective in Ehlers-Danlos disease. It is not affected by vitamin C deficiency.
Right Answer	RightAnswer::A
Explanation	[[Explanation::Scurvy is a relatively rare disease occuring in patients with severe Vitamin C deficiency. As vitamin C is needed in the hydroxylation of proline and lysine residues during collagen synthesis, its deficiency would lead to signs and symptoms of collagen abnormality. Patients initially complain of nonspecific malaise and fatigue that would progress to bony pain and dyspnea. Physical exam would reveal multiple bruises compatible with easy bruisability due to decreased collagen synthesis in the skin. Other signs include swollen gums, poor wound healing, and anemia. Scurvy is usually seen only in patients with very poor nutrition since vitamin C is redundantly present in most diets. Treatment is usually restricted to vitamin C supplementation and supportive care. Learning objective: Vitamin C is important in the hydroxylation of proline and lysine residues during collagen synthesis. Vitamin C deficiency lead to scurvy characterized by ecchymoses, swollen gums, and poor wound healing. Reference: Kumar V, Abbas AK, Fausto N, Aster JC. Environmental and nutritional diseases. In: Kumar V, Abbas AK, Fausto N, Aster JC, eds. Robbins and Cotran Pathologic Basis of Disease. 8th ed. Philadelphia, PA: Elsevier Saunders; 2009:chap 9. Educational Objective: References: ]]
Approved	Approved::No
Keyword	WBRKeyword::Scurvy, WBRKeyword::Vitamin C deficiency
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::