In lobstein disease or brittle bone disease defect occurs in:
**Question:** In Lobstein disease or brittle bone disease, defect occurs in:
1. Core Concept: Lobstein disease, also known as osteogenesis imperfecta type II, is a rare genetic disorder characterized by fragile bones that easily fracture. It is caused by mutations in the COL2A1 gene, which encodes type II collagen, a structural protein essential for maintaining bone and cartilage integrity.
2. Why the Correct Answer is Right: In this case, the correct answer (D) is related to the genetic defect causing Lobstein disease. Type II collagen is a crucial component of the extracellular matrix in cartilage and bone. Mutations in the COL2A1 gene lead to the production of a non-functional collagen type II protein, resulting in a deficiency of this essential protein in the bone matrix.
3. Why Each Wrong Option is Incorrect:
A. This option is incorrect because it pertains to another genetic disorder, osteogenesis imperfecta type I, characterized by increased bone density rather than fragility.
B. This option is incorrect because it refers to a defect in collagen type I, which is involved in the structure of bone and blood vessels, not bone fragility.
C. This option is incorrect as it pertains to a defect in the COL1A1 gene, which codes for collagen type I, not COL2A1, responsible for osteogenesis imperfecta type II.
4. Clinical Pearl: Lobstein disease is a rare autosomal dominant disorder, which means it can be inherited or occur spontaneously. The clinical manifestations include bone fragility, blue sclerae (blue eyes), and hearing loss.
5. Core explanation: The correct answer (D) highlights the genetic defect in Lobstein disease, which is characterized by mutations in COL2A1 gene causing a deficiency of collagen type II, leading to impaired bone and cartilage structure and function. This results in fragile bones, which is a hallmark feature of the disease.
6. Correct Answer: D. COL2A1 (The COL2A1 gene is responsible for encoding collagen type II, which is essential for maintaining the integrity of bone and cartilage in Lobstein disease.)