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nbme24/Block 2/Question#39

A 3-year-old boy has short stature and extremities ...

Endochondral ossification

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submitted by m-ice(127),

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.