In Congenital dystrophic epidermolysis bullosa, defect is in
**Core Concept**
Congenital dystrophic epidermolysis bullosa is a genetic disorder characterized by **blistering of the skin** due to minor trauma. The underlying cause involves defects in the anchoring fibrils that hold the epidermis to the dermis. This condition is related to the **collagen VII** gene.
**Why the Correct Answer is Right**
The correct answer is related to the **collagen VII** gene, which codes for a crucial component of **anchoring fibrils**. These fibrils are essential for the adhesion between the epidermis and dermis, and their deficiency leads to blister formation. The **COL7A1 gene** is specifically implicated in this condition.
**Why Each Wrong Option is Incorrect**
**Option A:** This choice is incorrect because it does not relate to the specific genetic defect in Congenital dystrophic epidermolysis bullosa.
**Option B:** Similarly, this option is incorrect as it is not associated with the anchoring fibril defect.
**Option D:** This choice is also incorrect as it does not correspond to the collagen VII defect.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that Congenital dystrophic epidermolysis bullosa is associated with significant **morbidity and mortality**, and early diagnosis is crucial. The condition can lead to **squamous cell carcinoma** in later life.
**Correct Answer:** D. Collagen VII.