USMLE Step 1 Question 312

Question:

A five-month old infant is brought to your office with a distressed mother. She complains that he bruises easily when on his back and arms when he is laid in his crib every night. She thinks his joints feel “loose” and that when she picks him up she is afraid that she may dislocate his shoulders. On exam his arms feature ecchymoses and cigarette-paper-like stretch marks on the skin. Which of the following is the likely defect causing this infant’s presentation?

Correct Answer: C.  Faulty collagen synthesis and misfolding

This infant is exhibiting a classical form of Ehlers-Danlos syndrome, characterized by hyperextensible joints and skin under physiologic loading, and a tendency to bleed, due to a defect in collagen synthesis and folding.

Sphingomyelinase deficiency is associated with Niemann-Pick disease.

A dynein arm defect resulting in immotile cilia is found in Kartagener’s syndrome.

The autosomal dominant fibrillin gene mutation is found Marfan’s disease.

Glycogen accumulation in the muscle tissue of infants and toddlers can be verified microscopically in McArdle’s disease, a disorder of glycogen storage.