Xeroderma pigmentosum (XP) predisposes to early skin cancers due to defective repair of UV-induced DNA damage. Which specific DNA repair pathway is defective in the most common XP complementation groups (XP-A to XP-G)?
- A Base excision repair (BER)
- B Mismatch repair (MMR)
- C Nucleotide excision repair (NER) ✓
- D Homologous recombination repair (HRR)
Correct answer: C. Nucleotide excision repair (NER)
Explanation
XP complementation groups A–G all have defects in nucleotide excision repair (NER), the pathway responsible for removing UV-induced bulky DNA adducts including cyclobutane pyrimidine dimers (CPDs) and 6–4 photoproducts. XP variant (XP-V) has defective translesion synthesis (polymerase eta). BER is defective in MUTYH-associated polyposis; MMR in Lynch syndrome; HRR in BRCA-mutated cancers.
Reference: Neena Khanna Illustrated Synopsis of Dermatology & STD, 6th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.