Xeroderma pigmentosa is 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 skin abnormalities.
**Why the Correct Answer is Right**
The correct answer is related to the deficiency of nucleotide excision repair (NER) pathway enzymes. In XP, mutations in genes involved in NER, such as XPC, XPD, XPF, XPG, ERCC1, and ERCC2, result in the inability to repair UV-induced DNA damage. This damage triggers mutations in genes that control cell growth, leading to cancer and other skin abnormalities.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not relate to the specific genetic defect causing XP. While oxidative stress is a factor in many diseases, it is not the primary cause of XP.
**Option B:** This option is incorrect because it refers to a different genetic disorder, Fanconi anemia, which is characterized by a deficiency in homologous recombination repair.
**Option C:** This option is incorrect because it is not directly related to the pathophysiology of XP. While DNA repair mechanisms are critical in many diseases, the specific defect in XP is related to NER, not base excision repair.
**Clinical Pearl / High-Yield Fact**
XP patients have an increased risk of skin cancers, including melanoma, and should avoid exposure to UV light. They may also experience other skin abnormalities, such as freckling, blisters, and scarring.
**Correct Answer: D. Deficiency in nucleotide excision repair (NER) pathway enzymes.**