Achondroplasia is an uncommon condition, and its recurrence risk depends on whether one or both of the parents has the disease.


Inheritance: autosomal dominant with high (100%) penetrance


Frequency: 1 in 15,000 to 1 in 40,000 live births


Parental status patterns:

(1) neither parent has clinical achondroplasia

(2) one parent normal, one parent with achondroplasia

(3) both parents with achondroplasia


Parental Status

Recurrence Risk

neither parent with achondroplasia (both normal)

99.98% normal

0.02% with achondroplasia

one parent with achondroplasia, second normal

50% normal

50% heterozygous for achondroplasia,

both parents with achondroplasia

25% normal

50% heterozygous for achondroplasia

25% homozygous



• The risk of recurrence in "sporadic" cases with phenotypically normal parents depends on the mutation rate and the occurrence of gonadal mosaicism (Mettler and Fraser). Because of gonadal mosaicism, the recurrence rate should be higher than twice that of the mutation rate (a rate of 1 in 20,000 would be 0.005%; 2 times this 0.01%).

• The risk of recurrence of "sporadic" cases appears related to a paternal age > 35 years of age.

• Homozygous achondroplasia is lethal as a neonate.


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