Autosomal dominant inheritance

Each gene has two copies

Traits (such as eye color or risk for disease) are passed to your children by genes. Each person has two genes for each trait. One gene is from the mother and one gene is from the father.

Autosomal dominant inheritance refers to conditions caused by changes (“mutations”) in genes located on one of the 22 pairs of autosomes. Autosomes are the numbered chromosomes that are the same in all males and females. Autosomal conditions occur in both men and women and are not related to whether a person is male or female.

“Affected” people inherit one changed copy

A parent with an autosomal dominant disorder will pass on either a changed copy of the gene or a normal copy of the gene to each of his or her children. In general, if a child inherits the changed copy of the gene, he or she is “affected” and therefore has the disorder.

A child who inherits normal (unchanged) copies of the gene will not inherit the disorder.

One changed copy “dominates”

A person needs to inherit only one changed copy of the gene pair in order to be affected with a specific autosomal dominant disorder. The changed copy “dominates” the pair of genes. In an autosomal dominant disorder, one changed copy from one parent causes the child to have the disorder.

Who is “affected”

A child who inherits the changed copy of the gene will have Marfan syndrome. People with Marfan can pass the changed gene to their children. A person with Marfan has a 1 in 2 (50 percent) chance of passing on the changed copy of the gene and a 1 in 2 (50 percent) chance of passing on the normal copy of the gene to each child.

So, there is a 50-50 chance that each child of a person with Marfan syndrome will inherit Marfan syndrome. This 50-50 chance is the same for each and every pregnancy.

Example: Marfan syndrome

An example of an autosomal dominant condition is Marfan syndrome. It is caused by a mutation in the fibrillin 1 (FBN1) gene. If a parent has Marfan syndrome, one copy of their FBN1 gene has a change (also called a mutation). The other copy of the FBN1 gene is normal (unchanged).