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NBME 23 Answers

nbme23/Block 2/Question#5

A female newborn develops respiratory distress. Her ...

Osteogenesis imperfecta, type I

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 +5  upvote downvote
submitted by seagull(734),

The underlying mechanism is usually a problem with connective tissue due to a lack of type I collagen. This occurs in more than 90% of cases due to mutations in the COL1A1 or COL1A2 genes. These genetic problems are often inherited from a person's parents in an autosomal dominant manner or occur via a new mutation.

-Wiki

Basically, good f***ing luck!





 +3  upvote downvote
submitted by hungrybox(443),

TLDR: Physical symptoms >> family history or anything else.

Like the other guy said, I got played hard.

I thought:

• poor prenatal care

• no family history

• bone problem/fractures

Instantly pointed to Rickets.

BUT, in retrospect this is key:

• intercostal retractions (vs. rachitic rosary → costchondral thickenings)

They're basically telling you to rule out Rickets. It seems 100% unfair b/c poor prenatal care seemed to rule in Rickets. The no family history seems to rule out OI.

But I guess what I've learned is, physical symptoms trump ANYTHING ELSE on NBMEs.





 +2  upvote downvote
submitted by nukie404(6),

At first I was thinking aha! Child abuse! But I guess wormian bones are more suggestive of OI, although the no family hx part was rather bleh.

thotcandy  Literally had it on OI until I saw no family hx... Isn't it AUTOSOMAL DOMINANT? +1  




How is this the answer if there is no family history of recurrent fractures? I thought osteogenesis imperfecta was autosomal dominant?

seagull  Exactly!! it's an autosomal dominate disease! +1  
emcee  Autosomal dominant diseases are variably expressive. Still, I think this was a badly written question (should have given us some family history). +  
wutuwantbruv  Also, FA says that fractures may occur during the birthing process, which is what I believe they were going for. I don't believe these findings would be seen at birth with any of the other choices. +  
d_holles  Yeah I thought I outsmarted NBME by selecting Rickets bc it said no family history ... guess I got played lol. +7  
jean_young2019  Could it be a sporadic cases? Spontaneous Mutation This is a change in a gene that occurs without an obvious cause, in a family where there is no history of the particular gene mutation. OI is inherited as an autosomal dominant trait. Approximately 35% of cases have no family history and are called "sporadic" cases. In sporadic cases, OI is believed to result from a spontaneous new mutation. http://www.oif.org/site/PageServer?pagename=Glossary +5  




So once you're down to OI and Rickets think about the pathogenesis of the two diseases and ignore the rest of the stem for a second. Bone is basically two parts. A fibrous "rebar" part and a calcium "cement" part. OI has defective type 1 collagen leading to bones that have no problem mineralizing (cement) but are lacking the rebar. This leads to super brittle bones that break all the time. Like hundreds of fractures.

Vit D deficiency causes an inability to mineralize but has no problem with laying down the collagen or "rebar". As a result you get soft and bendy bones. Sure they can break but the main problem is lack of strength.

From there you pick OI because the kid has 1000 fractures. Rickets wouldn't present that way.

Also bonus buzzword: apparently "wormian appearance" is an important diagnostic clue for OI.