If two parents have Achondroplasia what are the chances that their child will also have the disease?

Answer 1

Achondroplasia is autosomal dominant: it only takes one allele to have achondroplasia.

If the parents are of genotypes Aa and Aa (most likely), then each of their children has a 3/4 or 75% chance of having achondroplasia.

If either or both of the parents are homozygous AA, then all of the children would be expected to have the disease, 100%.

Answer 2

Achondroplasia is inherited in an autosomal dominant manner, therefore, if both parents have achondroplasia, the chance of normal stature in their offspring is 25%; of having achondroplasia, 50%; and of having homozygous achondroplasia (a lethal condition), 25%.

Note that over 80% of individuals with achondroplasia have parents with normal stature and have achondroplasia as the result of a de novo mutation in the FGFR3 gene.

The two links below will provide you with additional information.

A comment in response to ecolink's answer...
You can safely assume the parents with Achondroplasia are NOT homozygous. As I mentioned in my answer, the homozygous condition is usually lethal and if the offspring did survive, it would not survive into adulthood. Therefore a homozygous individual could not be a parent.

Answer 3

People with achondroplasia may pass on the condition to their children. If one parent is affected, each child has a one-in-two chance of having achondroplasia, and a one-in-two chance of being average height. Those born with achondroplasia may pass the condition on to their own children, while those of average height will not.