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?
- A)Defective nucleotide excision repairGABARITO
- B)Defective mismatch repair
- C)Defective base excision repair
- D)Defective homologous recombination of double strand breaks
- E)Defective nonhomologous end joining
Explicação
This child has xeroderma pigmentosum due to defective nucleotide excision repair. UV light induces pyrimidine dimers, and inability to excise and replace the damaged DNA leads to extreme photosensitivity and early skin cancers. The very early onset of multiple... Ver explicação completa e trilha adaptativa →