Noonan syndrome

Page last reviewed: 13/07/2011

Noonan syndrome is a genetic disorder that affects between one in 1,000 and one in 5,000 people. It is usually diagnosed at birth or in early childhood.

Noonan syndrome is named after Dr Jacqueline Noonan, a paediatric cardiologist (children's heart specialist) in the US. She noticed that many children attending her clinic with narrowing of the pulmonary valves were also short and had similar facial features.

The symptoms of Noonan syndrome can vary from person to person but there are several distinctive symptoms and physical features that many people with the disorder have in common. These include:

  • distinctive facial features,
  • short stature, and
  • heart defects.

The severity of Noonan syndrome can also vary enormously from one person to another.  Mild cases of the disorder often remain undiagnosed.

Genetic disorder
A genetic disorder is a disorder caused by a fault in the genes. It is usually hereditary (runs in the family).
The heart is a muscular organ. Its function is to pump blood around the body.

Page last reviewed: 13/07/2011

There are many different symptoms associated with Noonan syndrome and not everyone with the disorder will have all of them. The symptoms also vary in severity.

Heart defects

Around 80% of children with Noonan syndrome have heart defects. The most common heart defects are listed below.

  • Pulmonary valve stenosis: narrowing of the valve that takes blood from the heart to the lungs.
  • Hypertrophic cardiomyopathy: thickening of the heart muscles.
  • Ventricular septal defect: where there is a hole in between the lower two chambers of the heart.
  • Atrial septal defect: where there is a hole in between the upper two chambers of the heart.

Facial and physical features

The facial and physical features of Noonan syndrome tend to differ from person to person. As a person with the disorder gets older, the characteristic facial features are thought to become less noticeable.

The characteristic features of Noonan syndrome can include:

  • drooping eyelids (Ptosis),
  • large, downward slanting eyes,
  • widely spaced eyes (hyperterlorism),
  • strikingly blue or blue/green eyes,
  • low-set ears,
  • a flat bridge to the nose,
  • a wide forehead,
  • short neck with extra skin folds (webbing),
  • a round-shouldered look,
  • a low hairline on the back of the neck, 
  • breastbone deformity with a sunken chest (Pectus excavatum), and
  • a short stature in correct proportion.

Blood clotting and bruising

Research has shown that 65% of children with Noonan syndrome bruise easily due to a defect in the clotting of their blood. This means that if your child needs to have surgery or dental work, they need to be observed for longer than usual afterwards in case of bleeding.

Vision problems

It is important that all children with Noonan syndrome have regular eye examinations. This is because problems such as short-sightedness, squint and astigmatism are common among people with the disorder.


If your child has Noonan syndrome, you should have their teeth checked by your dentist at an early age, and then on a regular basis. Children with Noonan syndrome sometimes get their milk teeth later than normal and teething can occur in an irregular pattern. Milk teeth can also be lost earlier than usual.

Good oral hygiene is particularly important, as poor dental enamel in children with Noonan syndrome can potentially cause problems later on. Your dentist will be able to advise you about how to keep your child's teeth healthy.

You should inform your dentist that your child has Noonan syndrome and that they may have a problem with bleeding (see above).

Feeding and speech

Children with Noonan syndrome sometimes experience problems with feeding and speech. Problems with feeding can include:

  • sucking problems due to weak muscles in the mouth and sometimes a high, arched palate,
  • problems moving on to lumpy foods,
  • refusal to eat certain flavours or textures,
  • a weak chewing action that can lead to mealtimes taking longer than expected, and
  • projectile vomiting during or after meals.

Weak muscles in the mouth can also mean that some children with Noonan syndrome have slow speech development. Children with feeding or speech problems will usually be referred to a speech and language therapist for specialist advice and support.


Noonan syndrome is not often associated with severe learning difficulties. However, about 10% of children with Noonan syndrome will require level special education and support. Occasionally, a child with Noonan syndrome will also be diagnosed with an autistic spectrum disorder (ASD). ASD is a lifelong condition that affects how a person communicates with, and relates to, other people.

Children with Noonan syndrome are likely to be monitored by a paediatrician (a children's health specialist) because their development is often delayed.

Fertility and puberty

Puberty is often delayed in both boys and girls with Noonan syndrome. The average age for girls with Noonan syndrome to start menstruating is about 15. This can cause some emotional concerns for children with Noonan syndrome, but it is not thought to have any physical complications.

In around 60% of boys with Noonan syndrome, either one or both of their testes fail to descend into the scrotum (the bag that holds the testicles). It is important that this is corrected through surgery at an early age, to avoid reduced fertility in later life.


Blood supplies oxygen to the body and removes carbon dioxide. It is pumped around the body by the heart.

The heart is a muscular organ that pumps blood around the body.

Lungs are a pair of organs in the chest that control breathing. They remove carbon dioxide from the blood and replace it with oxygen.

Page last reviewed: 13/07/2011

Noonan syndrome is a congenital genetic disorder, which means that a child is born with the condition and inherits it from one of their parents.

Family history of Noonan syndrome

Around half of all people with Noonan syndrome have a known family history of the disorder. In these cases, one of the genes that is responsible for the condition is passed on to them from one of their parents.

Two genes that have been identified as being responsible for Noonan syndrome are:

  • the PTPN11 gene
  • the KRAS gene

However, the KRAS gene is only thought to be responsible for 2.5% of cases of Noonan syndrome. It is thought that there are also other genes associated with the disorder. Research into this is ongoing.

New gene mutations

In the other half of people with Noonan syndrome,  the disorder is caused by a 'new gene mutation'.

In these cases, there is no family history of Noonan syndrome but a gene changes (mutates) spontaneously for the first time. The reason why this mutation occurs is not yet fully understood.

Page last reviewed: 13/07/2011

Noonan syndrome is usually diagnosed by a paediatrician (a children's health specialist), who will take all the symptoms into account.

Blood test

It is possible to have a blood test to look for changes to the genes that are known to be responsible for Noonan syndrome (the PTPN11 gene and the KPAS gene). However, this is a specialised process and it can take between two to three months to get a result.

Many specialists do not recommend that a blood test is used to diagnose Noonan syndrome. This is because if the result is negative, it doesn't necessarily mean that your child doesn't have the condition.

Your child may have all the signs of Noonan syndrome but not be affected by one of the two genes (PTPN11 and KPAS) that are known to cause Noonan syndrome. This is why experts believe several other genes are also responsible for the disorder.


If you are pregnant and you have a family history of Noonan syndrome, it may be possible to have a high-resolution scan (ultrasonogram). This can help to identify features that may suggest your unborn baby has Noonan syndrome. However, there is no way of knowing for certain.


Blood supplies oxygen to the body and removes carbon dioxide. It is pumped around the body by the heart.

The heart is a muscular organ that pumps blood around the body.

Page last reviewed: 13/07/2011

There is no cure for Noonan syndrome. However, it is possible to treat certain aspects of the disorder.

Congenital heart defects

Heart defects can usually be treated, although treatment will depend upon what type of defect your child has. The most common heart defect among children with Noonan syndrome is pulmonary valve stenosis. Pulmonary valve stenosis can often be treated using a balloon valvoplasty. This is a procedure that is carried out under a general anaesthetic.

A thin hollow tube (catheter) is inserted into a vein in the child's leg, and then guided up into the heart. When the tube has been positioned inside the heart valve, a tiny balloon is inflated to open up and stretch the valve. After the valve has been opened up, the balloon can be deflated and removed.

Other heart defects can often be treated using medication and surgery. Speak to your specialist for more information about what treatment may be appropriate for your child's individual needs.

Surgery on the testes (orchidopexy)

Boys who are born with Noonan syndrome often have undescended testicles (one or both). If this is the case, surgery is usually required at an early age (during infancy) to bring them down into the scrotum. This surgical procedure is called an orchidopexy.

An orchidopexy is performed under a general anaesthetic. A small incision ismade in the child's groin. The testicle or testicles are then freed and repositioned in the scrotum.

Vision problems

Your child should have regular eye examinations (at least once a year). Noonan syndrome can cause vision problems, such as short-sightedness (myopia), squint (where the eyes are misaligned due to an imbalance in the eye muscles), and astigmatism (an eye condition that causes blurred vision).

If your child has vision problems, visiting your optometrist (optician) regularly will ensure that these problems are picked up early, and that they are treated accordingly, usually with corrective lenses.

Feeding and speech problems

In children with Noonan syndrome, weak muscles in the mouth can sometimes cause speech and feeding problems. If your child has speech and/or feeding problems, they may be referred to a speech therapist for help and support.

The speech therapist will work with you and your child to help them develop the muscles in their mouth and show them how to use them more effectively.

Development issues

If your child has developmental problems and needs to have extra support with their learning, they will be offered support in the form of special education. Your specialist or education provider will be able to discuss all the options with you in more detail.


Blood supplies oxygen to the body and removes carbon dioxide. It is pumped around the body by the heart.

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