Marfan syndrome is a disorder of the body's connective tissues, a group of tissues that maintain the structure of the body and support internal organs and other tissues.
Children usually inherit the disorder from one of their parents.
Some people are only mildly affected by Marfan syndrome, while others develop more serious symptoms.
Typical characteristics of Marfan syndrome include:
Marfan syndrome is hereditary, which means it can be passed to a child from a parent who's affected.
In around three-quarters (75%) of cases, Marfan syndrome is inherited from 1 parent.
The syndrome is autosomal dominant, which means a child can inherit it even if only 1 parent has the syndrome.
There's therefore a 1 in 2 (50%) chance that the child of a parent with Marfan syndrome will inherit the syndrome.
The gene defect leads to abnormal production of a protein called fibrillin, resulting in parts of the body being able to stretch abnormally when placed under any kind of stress.
The defective fibrillin gene also causes some bones to grow longer than they should.
This means a person with Marfan syndrome may be tall because their arms and legs grow longer than normal.
In the remaining quarter (25%) of cases, neither parent has the syndrome.
In these cases, the fibrillin gene changes (mutates) for the first time in the parent's egg or sperm.
The mutated gene can be passed on to the child, who will then go on to develop the syndrome.
Diagnosing Marfan syndrome can be difficult as the symptoms can vary significantly from person to person.
As the symptoms of Marfan syndrome do not always develop during childhood, it may not be identified until the teenage years.
In 99% of cases, a genetic test can be used to confirm a diagnosis of Marfan syndrome.
But it's an expensive process, as the gene can mutate in more than 3,000 different ways.
In most cases, a diagnosis of Marfan syndrome is based on a thorough physical examination and a detailed assessment of a person's medical and family history.
There's no cure for Marfan syndrome, so treatment focuses on managing the symptoms and reducing the risk of complications.
As Marfan syndrome affects several different parts of the body, you'll be treated by a team of different healthcare professionals.
You'll be closely monitored and any complications will be treated if they occur.
A serious problem caused by Marfan syndrome can occur if the heart and the aorta, the body's main artery, are significantly affected. This can lead to a lower life expectancy.
If you or your child has Marfan syndrome, your clinical team will pass information about you or your child on to the National Congenital Anomaly and Rare Diseases Registration Service (NCARDRS).
This helps scientists look for better ways to prevent and treat this condition.
You can opt out of the register at any time.
Although Marfan syndrome is rare, affecting about 1 in 5,000 people in the UK, it's one of the most common connective tissue disorders.
Men and women are affected equally.