Autosomal Dominant, Spontaneous New Mutation - Example

Pedigree

The autosomal dominant condition appeared in the third generation, in a single individual, with no prior family history. This affected person married another affected person, and the trait appeared in their offspring.

Achondroplasia

This is a form of short-limbed dwarfism in which height is reduced from long bone shortening. Affected persons are of normal intelligence and function normally -- they are just short. Like many disorders involving structural genes, it is autosomal dominant. However, since most cases occur when parents are of normal height, it is apparent that most cases of achondroplasia are due to spontaneous new mutations in the fibroblast growth factor receptor 3 (FGFR3) gene. If two persons with achondroplasia marry (another combination is unlikely) then 3/4 of their children can be expected to have achondroplasia -- but 1/4 will die in utero, because the homozygous condition is lethal, as can be seen in the last pregnancy of the affected couple at the far lower right.