Marfan syndrome - Causes of Marfan syndrome

Marfan syndrome is a connective tissue disorder that's usually inherited from one of your parents.

Connective tissue helps the body maintain its structure and provides support and structure to other tissue and organs.

Connective tissue is usually strong and resilient (elastic). It's made up of a number of proteins, including:

collagen
elastin
fibrillin

In people with Marfan syndrome, a genetic defect affects the production of fibrillin.

Fibrillin

Marfan syndrome is caused by a defective gene that stops your body making normal fibrillin. Genes are units of genetic material that you inherit from your parents.

Fibrillin is a protein that helps give your connective tissue its elasticity (to help it move and flex) and strength (to help support organs and other parts of your body).

Most people have lots of fibrillin in their:

bones, ligaments, tendons and cartilage
aorta (main artery)
eye tissue

If you have Marfan syndrome, you don't have enough fibrillin, which means that these parts of your body can stretch abnormally when put under any kind of stress.

The defective fibrillin gene also causes some of the bones in your body to grow longer than they should. People with Marfan syndrome are often tall because their arms and legs tend to grow longer than normal.

Inheriting Marfan syndrome

Most people with Marfan syndrome inherit the faulty gene from a parent who has the syndrome.

The syndrome is autosomal dominant, which means that a child can inherit it even if only one parent has the syndrome.

If you have Marfan syndrome, there's a one in two chance of passing it on to your child.

Spontaneous Marfan syndrome

Around a quarter of people with Marfan syndrome don't have a parent with the syndrome.

In such cases, the fibrillin gene mutates (changes) for the first time in the egg or sperm of the parent.

Although the parent won't have Marfan syndrome, the mutated gene can sometimes be passed on to the child, who may then go on to develop the syndrome.