Diagnosis of Noonan syndrome

How is Noonan syndrome diagnosed?

The diagnosis of Noonan syndrome is based on the person's clinical symptoms and signs. The specialist examines the person looking for the specific features of Noonan syndrome.

Individuals who have Noonan syndrome have normal chromosome studies. Four genes - PTPN11, SOS1, RADF1 and KRAS - are the only genes that are known to be associated with Noonan syndrome.

Approximately 50 percent of individuals with Noonan syndrome have mutations in the PTPN11 gene. Twenty percent of those with Noonan Syndrome have mutations in the SOS1. Mutations in the RAF1 gene account for between 10 and 15 percent of Noonan syndrome cases. About 5 percent of people with Noonan syndrome have mutations in the KRAS gene and usually have a more severe or atypical form of the disorder. The cause of Noonan syndrome in the remaining 10 to 15 percent of people with this disorder is not yet known. .

Source: NHGRI (NIH)1

   •   •   •

Back to: « Noonan syndrome

   •   •   •

Diagnosis

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

These include:

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 will not rule out Noonan syndrome.

Source: NHS Choices UK2

   •   •   •

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 otitis media 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 condition.

Source: NHS Choices UK3

   •   •   •

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 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.

Source: NHS Choices UK4

Genetic Tests for Noonan syndrome

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 will not rule out Noonan syndrome.

Source: NHS Choices UK5

   •   •   •

References

  1. Source: NHGRI (NIH): genome.gov/ 25521674/ learning-about-noonan-syndrome/ 
  2. Source: NHS Choices UK: nhs.uk/ conditions/ noonan-syndrome/ diagnosis/ 
  3. ibid.
  4. ibid.
  5. ibid.

   •   •   •

Note: This site is for informational purposes only and is not medical advice. See your doctor or other qualified medical professional for all your medical needs.