need help with your account or subscription? click here to email us (or see the contact page)
join telegramNEW! discord
jump to exam page:
search for anything ⋅ score predictor (โ€œpredict me!โ€)

Retired NBME 24 Answers

nbme24/Block 2/Question#39 (reveal difficulty score)
A 3-year-old boy has short stature and ...
Endochondral ossification ๐Ÿ” / ๐Ÿ“บ / ๐ŸŒณ / ๐Ÿ“–
tags:

 Login (or register) to see more


 +9  upvote downvote
submitted by โˆ—m-ice(370)
get full access to all contentpick a username

This boy has achondroplasia, which is caused by an autosomal dominant mutation in Fibroblast Growth Factor Receptor 3. FGF signaling is needed for proper cartilage function, and without it, the long bones of the body will not grow because the growth plate (made of chondrocytes) does not function. However, bones that undergo membranous ossification, like the bones of the head, will grow normally. This results in the patient having short extremities with a normal size trunk and large head relative to the limbs.

get full access to all contentpick a username
mumenrider4ever  Small edit, achondroplasia is due to constitutive activation (not inactivation) of FGFR3, which inhibits chondrocyte proliferation +11



 +3  upvote downvote
submitted by โˆ—madojo(212)
get full access to all contentpick a username

The answer is not osteoclast activity because that would be referring to osteopetrosis in which there is a defect in osteoclast activity and you have thick dense bones that fracture easily. Improper osteoclast activity could also refer to Pagets disease of the bone aka Osteitis deformans but I don't think that would present this young and would be more associated with bone remodeling problems and an increase in hat size, etc.

The head size isn't increased it just looks like a large head in comparison to the dwarfism because achondroplasia doesn't affect membranous bones of the head. Increased growth hormone synthesis would be acromegaly I think but that is seen in adults. Low nasal bridge = saddle nose.

TMI but in FA there's something called Laron syndrome which is AR, and a defective GH receptor so you have increased GH and would also see dwarfism and a saddle nose and prominent forehead but a small head circumference.

get full access to all contentpick a username

Would the answer choice "Tendon formation" be referring to Marfan's syndrome or osteogenesis imperfecta? Fibrillin vs collagen type 1? or are they both relevant?

+/- thotcandy(131)


Must-See Comments from nbme24

seagull on Intestinal mucosa
tissue creep on Ask the roommate not to smoke in the apartment
drdoom on Adenosine
seagull on Increased serum testosterone concentration
atstillisafraud on Lamins
niboonsh on Only cookies are independently associated ...
atstillisafraud on Scar formation
lamhtu on Decreased adherence
drachenx on Damage to the rectovaginal septum
drdoom on Intestinal mucosa
azibird on Coronavirus
lsmarshall on Organic acid metabolism disorder
sympathetikey on Inhalant abuse
tea-cats-biscuits on Eosinophils

search for anything NEW!