WBR0603
| Author | [[PageAuthor::Ayokunle Olubaniyi, M.B,B.S [1]]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Genetics, MainCategory::Pathology |
| Sub Category | |
| Prompt | [[Prompt::A 12 year old girl is brought to the clinic with low back pain. Her past medical history is composed of several bone fractures starting from age 6. There was a positive history of bone fractures in the family. The examination of the eye is shown in the picture below.
Which of the following also contain the defective tissue implicated in this condition?]] |
| Answer A | AnswerA::Hyaline cartilage |
| Answer A Explanation | AnswerAExp::Incorrect. Hyaline cartilage contains type II collagen |
| Answer B | AnswerB::Smooth muscle |
| Answer B Explanation | AnswerBExp::Incorrect. Smooth muscles contain type III collagen |
| Answer C | AnswerC::Dermis |
| Answer C Explanation | AnswerCExp::Correct. Dermis (skin) contains type I collagen |
| Answer D | AnswerD::Kidney |
| Answer D Explanation | AnswerDExp::Incorrect. Kidney contains type III collagen |
| Answer E | AnswerE::Basement membrane |
| Answer E Explanation | AnswerEExp::Incorrect. Basement membrane contains type IV collagen |
| Right Answer | RightAnswer::C |
| Explanation | [[Explanation::The girl in this vignette has a condition known as Osteogenesis Imperfecta. Osteogenesis imperfect a.k.a. brittle bone disease or "Lobstein syndrome" is an autosomal dorminant bone disorder characterized by brittle 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. Reference: First Aid text 2012, pg 82 |
| Approved | Approved::No |
| Keyword | WBRKeyword::Osteogenesis Imperfecta, WBRKeyword::collagen |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |
