WBR0603
| Author | [[PageAuthor::Ayokunle Olubaniyi, M.B,B.S [1] (Reviewed by Will Gibson)]] |
|---|---|
| Exam Type | USMLE Step 1 |
| Main Category | Genetics, Pathology |
| Sub Category | 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 | Hyaline cartilage |
| Answer A Explanation | Hyaline cartilage contains type II collagen |
| Answer B | Smooth muscle |
| Answer B Explanation | Smooth muscles contain type III collagen |
| Answer C | Dermis |
| Answer C Explanation | Dermis (skin) contains type I collagen |
| Answer D | Kidney |
| Answer D Explanation | Kidney contains type III collagen |
| Answer E | Basement membrane |
| Answer E Explanation | Basement membrane contains type IV collagen |
| Right Answer | C |
| 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 |
| Approved | Yes |
| Keyword | Osteogenesis imperfecta, Collagen, Musculoskeletal, Genetics, Bone, Bone fracture, Connective tissue |
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