USMLE-Rx Step 1 Qmax Challenge #1278

Check out today’s Step 1 Qmax Question Challenge.

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usmle-rx-step-1-qmax-challenge-1278A 30-year-old woman is found unconscious in her home by her husband. On arrival in the emergency department, she is noted to have thin, translucent skin over her abdomen with prominent varicose veins and many bruises on her shins. He denies any major medical problems in her past, though does report that she always seemed to “bruise really easily.” Her husband thinks the patient’s mother may have had similar problems with bruising, and also that she had “some sort of surgery” when her intestine was found to “have a hole in it.” An autopsy is performed, and an abnormality is discovered in the circle of Willis, similar to that shown in the image.

Which of the following proteins was most likely defective in this patient?

A. Fibrillin-1
B. Keratin 14
C. Type I procollagen
D. Type III procollagen
E. Type IV collagen


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9 thoughts on “USMLE-Rx Step 1 Qmax Challenge #1278”

  1. I think mutation in “Type III procollagen” would be the answer, and this patient is a case of “Ehlers–Danlos syndrome” which can be transmitted by “Autosomal Dominant” pattern ( Her mom had some manifestation probably diverticulosis) and Aneurism which is seen in this angiography.

  2. Correction of the above .
    Correct answer D : EDS vascular type follows autosomal dominant inheritance. Is caused by abnormal changes (mutations) of the gene known as collagen type III, alpha-1 (COL3A1), which is located on the long arm of chromosome 2 (2q31).

  3. EDS type IV is caused by a mutation in COL3A1 gene which makes type III procollagen. This is characterized by weakness in blood vessels and the bowel wall, which predisposes them to rupture. ANSWER:D

  4. Organ involvement and vascular involvement relate to type 3 collagen, which is defective in the vascular type of Ehlers-Danlos disease. So the answer would be D.

    Remark: the authors of the question speak of ‘procollagen’, but the defect in Ehlers-Danlos relates to tropocollagen (and thus not procollagen) which cannot form fibrils. Problems in procollagen relate more to osteogenesis imperfecta in which triple helix formation (formation of procollagen) is deficient.

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