Clinical Utility of Testing

Testing is often performed late in pregnancy following detection of short limbs by ultrasound to differentiate between heterozygous achondroplasia (viable fetus) and thanatophoric dysplasia (lethal). The distinction aids in directing the medical management of the delivery and helps prepare the family for an unfortunate outcome if the fetus has thanatophoric dysplasia. More rarely, testing may be performed in the first trimester because one parent has achondroplasia. If both parents have achondroplasia, prenatal testing can determine whether the fetus has lethal homozygous achondroplasia (25% risk), has heterozygous achondroplasia (50% risk), or does not have any FGFR3 mutation (25% risk) Note that achondroplastic parents may view heterozygous achondroplasia as the preferred outcome. Testing is performed neonatally to confirm a clinical diagnosis.

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