Autosomal Dominant Inheritance

The term autosomal means that the disease-causing mutation is located on one of the 22 autosomes. The term dominant has classically meant any person with one copy of a mutation would manifest symptoms of disease. However, geneticists now recognize that for some autosomal dominant conditions, people can have a mutation and still not develop disease. Two explanations for this phenomenon exist: reduced penetrance and variable expressivity. An individual with an autosomal dominant mutation has a 50% chance with each pregnancy to pass the mutation onto his or her child, without regard to the sex of the child.

When constructing a pedigree (a 3-generation medical family history) for a patient with an autosomal dominant condition, it is common to find relatives in many generations who also have the condition. For autosomal dominant conditions, only children of individuals with an autosomal dominant mutation will inherit the mutation. Children of parents without a mutation will not inherit a mutation.

• Males can transmit the condition to males (father to son).

• Males and females are equally likely to transmit the condition (to children of either gender).

• Males and females are both affected, usually in equal proportions (if there are enough people in the pedigree).

• The condition appears in multiple successive generations (vertical inheritance pattern).

• Each child of an affected parent has a 50% chance of being affected, provided the other parent is unaffected. Thus, half of the children of an affected individual are affected on average (may vary considerably due to statistical chance).

• Unaffected individuals do not have affected children.