WBR0603

Author	[[PageAuthor::Ayokunle Olubaniyi, M.B,B.S [1] (Reviewed by Will Gibson)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Genetics, MainCategory::Pathology
Sub Category	SubCategory::Musculoskeletal/Rheumatology
Prompt	[[Prompt::A 12 year old girl is brought to the clinic with lower back pain. Her past medical history is remarkable for several bone fractures starting from age 6. There is also a family history of bone fractures. Her eyes are pictured below. Which of the following also contain the defective tissue implicated in this patient's condition?]]
Answer A	AnswerA::Hyaline cartilage
Answer A Explanation	AnswerAExp::Hyaline cartilage contains type II collagen
Answer B	AnswerB::Smooth muscle
Answer B Explanation	AnswerBExp::Smooth muscles contain type III collagen
Answer C	AnswerC::Dermis
Answer C Explanation	AnswerCExp::Dermis (skin) contains type I collagen
Answer D	AnswerD::Kidney
Answer D Explanation	AnswerDExp::Kidney contains type III collagen
Answer E	AnswerE::Basement membrane
Answer E Explanation	AnswerEExp::Basement membrane contains type IV collagen
Right Answer	RightAnswer::C
Explanation	[[Explanation::The girl in this vignette has a condition known as Osteogenesis Imperfecta (OI). Osteogenesis imperfect (also known as brittle bone disease or "Lobstein syndrome") is an autosomal dominant bone disorder characterized by bones that are prone to fracture. People with OI are born with defective connective tissue, or without the ability to make it, usually because of a mutation in the genes coding for type-I pro-collagen i.e. COL1A1 and COL1A2. There are seven subtypes varying in severity, age of presentation, and clinical features. Classic signs and symptoms include: fractures after minor trauma, blue tint of the white part of the eye and deafness. Type I collagen is found in bone, skin (dermis), tendon, dentin, fascia, cornea, late wound repair/mature scar, fibrous cartilage Type II – Hyaline and elastic cartilage, vitreous body, nucleus pulposus Type III – Skin, blood vessels, uterus, smooth muscle, liver, kidney, lung, spleen, fetal tissue, granulation tissue/early wound repair Type IV – Basement membrane Educational Objective: Defective type I collagen found in Osteogenesis Imperfecta is responsible for the brittle bones, lax ligaments and tendons. The characteristic blue-gray sclera is pathognomonic. References: Forlino, Antonella, et al. "New perspectives on osteogenesis imperfecta." Nature Reviews Endocrinology 7.9 (2011): 540-557. First Aid 2015 page 76]]
Approved	Approved::Yes
Keyword	WBRKeyword::Osteogenesis imperfecta, WBRKeyword::Collagen, WBRKeyword::Musculoskeletal, WBRKeyword::Genetics, WBRKeyword::Bone, WBRKeyword::Bone fracture, WBRKeyword::Connective tissue
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