Medical Genetics

Autosomal Dominant: Marfan Syndrome

Genes are inherited from our biological parents in specific ways. One of the basic patterns of inheritance of our genes is called autosomal dominant inheritance.

What is autosomal dominant inheritance?

Autosomal dominant inheritance means that the gene is located on one of the autosomes (chromosome pairs 1 through 22). This means that males and females are equally affected, and "dominant" means that only one gene is necessary to have the trait. When a parent has a dominant trait, there is a 50 percent chance that any child they have will also inherit the trait:

There are four possible combinations in the children. Two of the four, or 50 percent, have inherited the trait. The other 50 percent have not inherited the trait. These four combinations are possible every time a pregnancy occurs between these two individuals. The gender of the children (whether they are sons or daughters) does not matter. The chance is 50/50 for each pregnancy.

What is Marfan syndrome?

Marfan syndrome occurs in one in 5,000 live births and is a connective tissue disorder associated with autosomal dominant inheritance. Connective tissue is abundant in the body and is important as a supporting structure, principally for the musculoskeletal system but for other body systems as well, including the eyes and heart. The gene for Marfan syndrome, called fibrillin-1, is localized to chromosome #15 on the long arm (q) at 15q21.1.

Common findings include those related to abnormalities in connective tissues, such as abnormal enlargement of the aortic root of the heart, dislocated lenses of the eyes, and a tall, lanky body with increased joint mobility, scoliosis, long flat feet, and long fingers. Findings may vary among individuals diagnosed with this condition, even within a family.

If an individual carries an abnormal gene for Marfan syndrome, that individual has a 50 percent risk for occurrence of Marfan syndrome with each future pregnancy. If a person does not carry the gene abnormality, then the risk for occurrence of the disorder in future offspring would be the same as the population risk.