A patient presents with extreme photosensitivity, numerous skin cancers at an early age, and neurological abnormalities. Genetic testing reveals a defect in a DNA repair pathway responsible for excising bulky adducts, such as pyrimidine dimers formed by UV radiation. Which repair mechanism is most likely impaired?

The correct answer to the question "A patient presents with extreme photosensitivity, numerous skin cancers at an early age, and neurological abnormalities. Genetic testing reveals a defect in a DNA repair pathway responsible for excising bulky adducts, such as pyrimidine dimers formed by UV radiation. Which repair mechanism is most likely impaired?" is Option B: Nucleotide excision repair.

The other options — A) Base excision repair, C) Mismatch repair, D) Non-homologous end joining — are incorrect for this USMLE Exam Prep question. As explained above: Xeroderma Pigmentosum is characterized by a defect in Nucleotide Excision Repair (NER), a critical pathway for removing bulky DNA lesions such as pyrimidine dimers induced by UV light. This leads to …