Molecular Biology/Genetics USMLE Step 1 Practice Question
An 8-year-old boy presents with severe photosensitivity and multiple freckle-like pigmented lesions on sun-exposed areas. Vital signs are normal; however, he has already undergone excision of two basal cell carcinomas. Laboratory studies reveal unrepaired thymine dimers after UV exposure. He denies neurologic symptoms. His parents report he wears protective clothing and sunscreen daily but continues to develop cutaneous malignancies at an unusually early age. Which of the following DNA repair pathway defects most likely explains his clinical presentation?
Answer choices
- ADefective nucleotide excision repairCorrect answer
- BDefective mismatch repair
- CDefective base excision repair
- DDefective homologous recombination of double strand breaks
- EDefective nonhomologous end joining
- FAtaxia-telangiectasia
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