Noonan syndrome can affect a person in many different ways. Not everyone with the condition will share the same characteristics.

The 3 most common characteristics of Noonan syndrome are:

• unusual facial features
• short stature (restricted growth)
• heart defects present at birth (congenital heart disease)

Unusual features

People with Noonan syndrome may have a characteristic facial appearance, although this isn't always the case.

The following features may become apparent soon after birth:

• a broad forehead
• drooping eyelids (ptosis)
• a wider-than-usual distance between the eyes
• a short, broad nose
• low-set ears that are rotated towards the back of the head
• a small jaw
• a short neck with excess skin folds
• a lower-than-usual hairline at the back of the head and neck

Children with Noonan syndrome also have abnormalities that affect the bones of the chest. For example, their chest may stick out or sink in, or they may have an usually wide chest with a large distance between the nipples.

These features may be more obvious in early childhood, but tend to become much less noticeable in adulthood.

Short stature

Children with Noonan syndrome are usually a normal length at birth. However, at around 2 years old you may notice that they don't grow as quickly as other children of the same age.

Puberty (when a child begins to mature physically and sexually) typically occurs a few years later than normal, and the expected growth spurt that usually happens during puberty is either reduced or doesn’t happen at all.

Medication known as human growth hormone can sometimes help children reach a more normal height. Left untreated, the average adult height for men with Noonan syndrome is 162.5cm (5ft 3in) and for women is 153cm (5ft).

Heart defects

Most children with Noonan syndrome will have some form of congenital heart disease. This is usually one of the following:

• pulmonary valve stenosis – where the pulmonary valve (the valve that helps control the flow of blood from the heart to the lungs) is unusually narrow, which means the heart has to work much harder to pump blood into the lungs
• hypertrophic cardiomyopathy – where the muscles of the heart are much larger than they should be, which can place a strain on the heart
• septal defects – a hole between 2 of the chambers of the heart (a "hole in the heart"), which can cause the heart to enlarge and/or lead to high pressure in the lungs

Read more about the different types of congenital heart disease.

Other characteristics

Other less common characteristics of Noonan syndrome can include:

• learning disability – children with Noonan syndrome tend to have a slightly lower-than-average IQ and a small number have learning disabilities, although these are often mild
• feeding problems – babies with Noonan syndrome may have problems sucking and chewing, and may vomit soon after eating
• behavioural problems – some children with Noonan syndrome may be fussy eaters, behave immaturely compared to children of a similar age, have problems with attention and have difficulty recognising or describing their or other people’s emotions
• increased bruising or bleeding – sometimes the blood doesn't clot properly, which can make children with Noonan syndrome more vulnerable to bruising and heavy bleeding from cuts or medical procedures
• eye conditions – including a squint (where the eyes point in different directions), a lazy eye (where one eye is less able to focus) and/or astigmatism (slightly blurred vision caused by the front of the eye being an irregular shape)
• hypotonia – decreased muscle tone, which can mean it takes your child a bit longer to reach early developmental milestones
• undescended testicles – in boys with Noonan syndrome, one or both testicles may fail to drop into the scrotum (sac of skin that holds the testicles)
• infertility – particularly if undescended testicles aren't corrected at an early age, there's a risk of boys with Noonan syndrome having reduced fertility; fertility in girls is usually unaffected
• lymphoedema – a build-up of fluid in the lymphatic system (a network of vessels and glands distributed throughout the body)
• bone marrow problems – a small number of people can develop an abnormal white blood cell count; this can sometimes get better on its own, but can occasionally turn into leukaemia

A variety of different tumours (cancerous growths) have also been found in people with Noonan syndrome, but it’s often not clear if these are caused by the condition or occur by chance.

Overall, the risk of developing cancer doesn't appear to be much higher than for people without Noonan syndrome, although there may be a very small increased risk of some rare childhood cancers.

Noonan syndrome is caused by a faulty gene, which is usually inherited from one of the child's parents.

There's no evidence to suggest the genetic fault is caused by environmental factors, such as diet or exposure to radiation.

Noonan syndrome genes

Faults in at least 8 different genes have been linked to Noonan syndrome. The most commonly altered genes are:

• the PTPN11 gene
• the SOS1 gene
• the RIT1 gene
• the RAF1 gene
• the KRAS gene

In around 1 in 5 cases, no specific genetic fault can be found.

The symptoms of Noonan syndrome are generally similar, no matter which gene is affected.

However, the faulty PTPN11 gene is commonly associated with pulmonary stenosis (a narrowed heart valve) and the faulty RAF1 gene is more often associated with cardiomyopathy (disease of the heart muscle).

Read more about the characteristics of Noonan syndrome.

How Noonan syndrome is inherited

In around 30-75% of cases, Noonan syndrome is inherited in what's known as an autosomal dominant pattern.

This means that only one parent has to carry a copy of one of the faulty genes to pass it on, and each child they have will have a 50% chance of being born with Noonan syndrome. The parent carrying the faulty gene will also have the condition themselves, although it may be very mild.

In the remaining cases, the condition is caused by a new genetic fault that isn't inherited from either parent.

What are the chances of having another child with the syndrome?

If you have a child with Noonan syndrome and neither you or your partner have been diagnosed with it yourselves, talk to your GP about getting a referral to a genetic counsellor.

You may be able to have a genetic blood test to see if either of you carry one of the faulty genes associated with the condition.

If neither of you carry one of the faulty genes, the risk of having another child with the condition is very small (estimated to be less than 1%).

If one of you does carry a faulty gene or has been diagnosed with Noonan syndrome, there's a 50% risk of each further child you have being born with the condition.

A genetic counsellor can explain the risks and your options for having another child. These may include:

• having a test during pregnancy to see if your baby will have Noonan syndrome
• adopting a child
• having a child with a donor egg or sperm
• pre-implantation genetic diagnosis – where eggs are fertilised and tested in a laboratory, and only eggs without the faulty Noonan syndrome genes are implanted in the womb

Read more about diagnosing Noonan syndrome.

Noonan syndrome may be suspected if your child has some of the signs and symptoms associated with the condition.

These include:

• distinctive facial features
• short stature (restricted growth)
• a mild learning disability
• undescended testicles 
• lymphoedema

Read more about the characteristics of Noonan syndrome.

However, these symptoms can have a number of different causes, so it's difficult to make a diagnosis based on them alone.

You may be referred to a genetics specialist for genetic testing. In most cases, Noonan syndrome can be confirmed by a blood test for the various genetic mutations. However, in about 1 in 5 cases no specific mutation can be found, so a negative blood test won't rule out Noonan syndrome.

Further testing

If Noonan syndrome has been confirmed or is strongly suspected, further tests are needed to establish the extent of the symptoms. These tests may include:

• an electrocardiogram (ECG) – where electrodes (small, metallic discs placed on the skin) measure the electrical activity of the heart
• an echocardiogram – an ultrasound scan of the heart
• an educational assessment
• blood tests to check how well the blood clots
• eye tests – to check for problems such as squints or blurred vision
• hearing tests – to check for problems such as hearing loss caused by a middle ear infection or damage to the cells or nerves inside the ear

Some of these tests may need to be repeated regularly after the diagnosis, to monitor the symptoms.

Diagnosis during pregnancy

If you're pregnant, it may be possible to test your unborn baby for Noonan syndrome if:

• you, your partner or a close family member has been found to carry one of the faulty genes associated with the condition
• routine ultrasound scans detect possible signs of the condition in your baby, such as polyhydramnios (an excessive amount of amniotic fluid), pleural effusion (fluid in the space around the lungs) or a build-up of fluid in certain other parts of the body

Testing for Noonan syndrome during pregnancy involves collecting a sample of your baby's DNA and checking it for any of the faulty genes associated with the condition.

This can be done using either chorionic villus sampling (where a sample of cells is removed from the placenta) or amniocentesis (where a sample of amniotic fluid is removed). Both of these tests carry around a 0.5 to 1% chance of causing a miscarriage.

If your baby is found to have one of the faulty genes, a genetic counsellor will talk to you about what the test result means and what your options are. Read more about genetic testing and counselling.

There's no single treatment for Noonan syndrome, but it's possible to treat many aspects of the condition.

Your child may initially need quite a lot of treatment and support to help manage the various problems they have. However, they'll typically need much less care as they get older.

Although they'll probably need to have some routine tests and checks to monitor their symptoms, most adults with Noonan syndrome can lead a normal life.

Heart defects

A full assessment of your child's heart function should be carried out when Noonan syndrome is diagnosed. This will help determine whether they have any type of congenital heart disease.

The treatment your child needs will depend on the type of heart defect they have and how severe it is. For example:

• pulmonary stenosis may not need any treatment if it's mild, but more severe cases may require an operation to widen the narrowed heart valve or replace it with a new valve
• hypertrophic cardiomyopathy may need to be treated with medication such as beta-blockers or surgery to remove or destroy some of the excess heart muscle
• septal defects may not need any treatment if they're small because they may get better with age, but more severe cases may require an operation to seal the hole in the heart

Regular tests to check heart function will usually be carried out into adulthood.

Read more about treating congenital heart disease.

Restricted growth

Your child's size and growth rate will be regularly assessed throughout their childhood. If their growth rate is thought to be seriously reduced, treatment with human growth hormone may be suggested.

Treatment usually starts at around 4 or 5 years of age and continues until your child stops growing. A medication called somatropin is most often used. This is given as a single daily injection.

Side effects of somatropin are uncommon, although your child is likely to experience some temporary soreness, itchiness and redness at the site of the injection.

Read more about treating restricted growth.

Feeding and speech problems

In children with Noonan syndrome, weak muscles in the mouth can sometimes cause speech and feeding problems. They may be referred to a speech therapist for help and support.

The speech therapist will help your child develop the muscles in their mouth and try to teach them how to use their muscles more effectively.

In particularly severe cases of poor feeding, your baby may need a feeding tube for a few months.

Undescended testicles

If you have a baby boy with an undescended testicle, or testicles that don't descend naturally within a few months of birth, corrective surgery is usually recommended.

This is normally carried out before 2 years of age, because treating the problem early on should increase the chances of fertility being unaffected.

A surgical procedure known as an orchidopexy is the usual treatment for undescended testicles. It involves making a small cut in your child’s tummy or groin and moving the testicle(s) into the correct position.

Read more about treating undescended testicles.

Learning disabilities

If your child is diagnosed with a learning disability, it doesn't necessarily mean they can't be taught in a mainstream school. However, children with more severe disabilities may benefit from attending a specialist school.

To ensure your child gets the support they need, an Education, Health and Care (EHC) plan may need to be drawn up. This is a type of care plan designed to meet your child's health and educational requirements.

Read more about special educational needs and the assessment procedure.

Other health conditions

Find out about the treatment for some of the other problems that can affect people with Noonan syndrome:

• treating astigmatism 
• treating hypotonia 
• treating lazy eye 
• treating lymphoedema 
• treating a squint