Molecular Biology/Genetics USMLE Step 1 Practice Question
A 20-week gestation fetus is delivered after spontaneous abortion. Physical examination reveals microcephaly, microphthalmia, cleft lip and palate, polydactyly (six fingers bilaterally), and dextrocardia. Maternal history is significant for poorly controlled diabetes mellitus (HbA1c 10.2%) throughout the first trimester. Maternal serologies are negative for TORCH infections. Which chromosomal abnormality most likely accounts for this constellation of congenital malformations?
Answer choices
- ATrisomy 21
- BTrisomy 18
- C45,XO
- D5p-
- ETrisomy 13Correct answer
- FMaternal diabetes mellitus type 2 with poor glycemic control
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.