Xeroderma pigmentosum (XP) patients develop multiple skin cancers with minimal UV exposure. Cells from classic XP fail to remove pyrimidine dimers formed by UV radiation. The DNA repair pathway that is specifically defective in XP is:
- A Base excision repair (BER)
- B Nucleotide excision repair (NER) ✓
- C Mismatch repair (MMR)
- D Non-homologous end joining (NHEJ)
Correct answer: B. Nucleotide excision repair (NER)
Explanation
Nucleotide excision repair (NER) is the pathway responsible for removing bulky helix-distorting lesions, including UV-induced cyclobutane pyrimidine dimers and 6-4 photoproducts. XP is caused by mutations in any of the eight XP genes (XPA-XPG and XPV), most of which encode proteins of the NER machinery — including damage recognition (XPC-RAD23B), helix unwinding (XPD/ERCC2 helicase, part of TFIIH), dual incision, and gap filling. XPV encodes DNA polymerase eta, a translesion synthesis polymerase; its loss results in the variant form of XP.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.