WBR0646
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| Author | [[PageAuthor::Serge Korjian M.D. (Reviewed by Serge Korjian)]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Biochemistry |
| Sub Category | SubCategory::Dermatology, SubCategory::General Principles |
| Prompt | [[Prompt::A 4-year-old girl presents to the emergency room for 2 episodes of blood in the stools. History is initially inconclusive, but further questioning reveals that the child was recently diagnosed with a rare disorder that causes her to have hyperelastic skin and hyperextensible joints. Considering this patient has a mutation in type 1 collagen, what co-factor is essential in the defective enzyme in this patient?]] |
| Answer A | AnswerA::Selenium |
| Answer A Explanation | AnswerAExp::Selenium is a known cofactor for thyroid hormone deiodinases. It has no function with lysyl-oxidase. |
| Answer B | AnswerB::Niacin |
| Answer B Explanation | AnswerBExp::Niacin also known as vitamin B3 is an important cofactor for hydrogen transfer processes as NAD and NADP. It has no function with lysyl-oxidase. |
| Answer C | AnswerC::Zinc |
| Answer C Explanation | AnswerCExp::Zinc is very important in the formation of zinc fingers which constitute parts of some transcription factors. It has no function with lysyl-oxidase. |
| Answer D | AnswerD::Copper |
| Answer D Explanation | AnswerDExp::Copper is important for the proper functioning of lysyl-oxidase an enzyme defective in certain forms of Ehlers-Danlos syndrome. |
| Answer E | AnswerE::Biotin |
| Answer E Explanation | AnswerEExp::Biotin functions as a cofactor for carboxylation reactions (Acetyl-CoA carboxylase, methylcrotonyl-CoA carboxylase, and propionyl-CoA carboxylase). It has no function with lysyl-oxidase. |
| Right Answer | RightAnswer::D |
| Explanation | [[Explanation::Ehlers-Danlos Syndrome is a rare inherited disease that is heterogeneous in presentation and pathologic mechanisms. Six subtypes of Ehlers-Danlos exist with each having distinct mutations affecting collagen synthesis. One of the most studied pathological mechanisms of Ehlers-Danlos is a mutation affecting lysyl-oxidase, an enzyme responsible for collagen crosslinking in the extracellular matrix. Lysyl-oxidase requires copper as a cofactor to function effectively. Ehlers-Danlos classically presents with skin hyperextensibility, cutaneous fragility, joint hypermobility, and vascular anomalies. Educational Objective: Ehlers-Danlos is a rare inherited disorder with certain forms characterized by defective corss-linking of collagen fibers due to abnormal lysyl-oxidase. Lysyl oxidase requires copper as a cofactor. |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Ehlers-Danlos Syndrome, WBRKeyword::Collagen sythesis, WBRKeyword::Lysyl oxidase, WBRKeyword::Copper, WBRKeyword::Collagen, WBRKeyword::Ehlers-Danlos |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |