Xeroderma pigmentosum is caused due to:
**Core Concept**
Xeroderma pigmentosum (XP) is a rare genetic disorder characterized by an inability to repair DNA damage caused by ultraviolet (UV) light from the sun or other sources. This leads to an increased risk of skin cancers and other complications. The underlying defect in XP involves the nucleotide excision repair (NER) pathway, which is essential for repairing DNA damage caused by UV radiation.
**Why the Correct Answer is Right**
The correct answer is related to the defective gene responsible for XP. Specifically, XP is caused by mutations in genes involved in the NER pathway, including **XPA**, **XPC**, **XPD**, **XPF**, **XPG**, and **ERCC1** and **ERCC2**. These genes encode proteins that play a crucial role in recognizing and repairing DNA damage caused by UV radiation. In XP, the mutations in these genes result in a deficiency of NER, leading to an accumulation of DNA damage and an increased risk of skin cancers.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not specify the correct gene responsible for XP. While it may be related to the NER pathway, it is not the correct answer.
* **Option B:** This option is incorrect because it is not a known gene associated with XP. It may be a distractor to test the student's knowledge of other genetic disorders.
**Clinical Pearl / High-Yield Fact**
XP is a rare genetic disorder that highlights the importance of DNA repair mechanisms in maintaining genome stability. The NER pathway is a critical mechanism for repairing DNA damage caused by UV radiation, and defects in this pathway can lead to an increased risk of skin cancers and other complications.
**Correct Answer: C. Defects in nucleotide excision repair genes (XPA, XPC, XPD, XPF, XPG, ERCC1, and ERCC2)**