Achondroplasia is one of the most common and recognized short-limbed skeletal dysplasias, with a prevalence of 1 in 26,000 to 28,000 live births. Although achondroplasia is inherited in an autosomal dominant manner, 80% of affected children have a de novo mutation. The FGFR3 gene is the only gene associated with achondroplasia. Two mutations in this gene account for 99% of cases; both result in an amino acid change (glycine to arginine), which results in continuous activation of the FGFR3 protein. Having a constantly active FGFR3 protein leads to the inhibition of chondrocyte proliferation, which, in turn, inhibits bone growth. The average adult height for patients with achondroplasia is 131 cm for a man and 124 cm for a woman.

Achondroplasia should be considered prenatally if shortened long bones (usually <5th percentile) are noted on third trimester ultrasonography. Some studies have seen a distinctive “collar hoop” sign wherein there is a...

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