Marfan syndrome - Causes 

Marfan syndrome is a condition that affects the connective tissue. Connective tissue is used by the body to help maintain its structure and to provide support and structure to other tissue and organs.

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

• collagen
• elastin
• fibrillin

These proteins are usually produced by the body, but 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 from making fibrillin. Genes are units of genetic material that you inherit from your parents. Fibrillin is a protein that helps give your connective tissue:

• elasticity to help it move and flex
• strength to help it support organs and other parts of your body

Most people have lots of fibrillin in their:

• bones
• aorta (main artery)
• eye tissue

If you have Marfan syndrome, you do not 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. This gives people with Marfan syndrome a tall appearance 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 already has the condition. Marfan syndrome is an autosomal dominant condition. This means that a child can inherit the syndrome even if only one parent has the condition. 

Therefore, if you have Marfan syndrome, you have a one in two chance of passing the condition on to your child.

Spontaneous Marfan syndrome

Around a quarter of people with Marfan syndrome do not have a parent with the condition.

In such cases, the fibrillin gene mutates (changes) for the first time in the egg or sperm of the parent. Although the parent will not have Marfan syndrome, the mutated gene can sometimes be passed on to the child, who may then go on to develop the condition.