Diagnosis - 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
• heart problems
• a family history of Noonan syndrome

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.