Molecular Biology/Genetics USMLE Step 1 Practice Question
A 45-year-old kidney transplant recipient on tacrolimus and mycophenolate presents with fever (38.9°C), malaise, and floaters with hemorrhagic retinitis on fundoscopy. Labs show leukopenia (WBC 2.8) and positive CMV PCR (8,200 copies/mL). He initially improves on ganciclovir but develops recurrent symptoms after 6 weeks with rising viral load (15,000 copies/mL) despite documented adherence. No opportunistic infections noted. Which viral enzyme mutation most commonly explains ganciclovir resistance?
Answer choices
- AThymidine kinase
- BDNA dependent RNA polymerase
- CReverse transcriptase
- DUL97 phosphotransferaseCorrect answer
- ENeuraminidase
- FUL54 DNA polymerase mutation
See the full explanation
Get the correct-answer rationale, why each distractor is wrong, the underlying mechanism, and high-yield associations — plus adaptive practice that targets your weak areas — with a free MedBoardPRO account.