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NBME 17 Answers

nbme17/Block 4/Question#36 (reveal difficulty score)
A male newborn has macrocephaly with poor ...
Collagen ๐Ÿ” / ๐Ÿ“บ / ๐ŸŒณ / ๐Ÿ“–
tags: biochem msk

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 +7  upvote downvote
submitted by โˆ—waitingonprometric(264)
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I think that this is osteogenesis imperfecta based on the hx of several fractures that occurred during birth.

From FA2019, pg. 51: Manifestations can include--multiple fractures with bone deformities and minimal trauma; may occur during the birth process

OI is caused by gene defects in COL1A1 and COL1A2; most common form is autosomal dominant with decreased production of normal type 1 collagen.

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cheesetouch  FA2018 P 51 +
peteandplop  If you've ever seen Unbreakable, the main villain (Mr. Glass) has OI and is born with many broken bones--memorable scene to remember this disease (https://youtu.be/5E69-oJ7TDc?t=100); Other memory device, OI = bONEs for Collagen Type ONE +11
jurrutia  But what explains the poor skull mineralization? OI does not affect mineralization. +
lukin4answer  @jurrutia poor mineralization due to defective osteoid matrix. Osteoid composed of Col I. +1



 -1  upvote downvote
submitted by โˆ—soccerfan23(7)
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I believe that patient has achondroplasia because the short limbs and macrocephaly are a sign of failed endochondral ossification where cartilage is laid down by chondrocytes before it is converted into woven bone. Since cartilage is made out of collagen, that's the answer.

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neoamin  it's the one I thought of but I don't think the patient would have fractures at birth. +
blastocyte101  I think the misshaped long bones is such a distractor +



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