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USMLE · Question #531
USMLE Question #531: Real Exam Question with Answer & Explanation
The correct answer is B. It is a polymorphism. See the full explanation below for the reasoning.
Question
A 10-year-old girl is brought to the office by her mother because her school nurse thinks that she may have Marfan syndrome. She is at the 95 percentile for th height and 25 percentile for weight. Physical examination shows a narrow palate with dental crowding, long slender extremities, and joint laxity. Molecular testing for FBN1 shows a single nucleotide difference that does not change the amino acid at that locus. Her mother is 163 cm (5 ft 4 in) tall. There is no clinical evidence of Marfan syndrome in the mother, but she has the same single nucleotide change as the patient. The same nucleotide change is found in 15 of 200 individuals without Marfan syndrome. Which of the following best describes the single nucleotide change in the patient and her mother?
Options
- AIt is a disease-causing mutation in the patient and her mother
- BIt is a polymorphism
- CIt is a sequence variant of unknown significance
- DIt will change the folding of the protein
- EIt will result in a truncated protein
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