Noonan syndrome (NS)

What is Noonan syndrome?

Noonan syndrome is one of the more common genetic disorders, affecting 1 in 1000–2500 births.

Noonan syndrome affects multiple parts of the body but can look very different from person to person. People with Noonan syndrome typically have certain distinct facial features, heart defects and short stature. It’s present from birth but may not be diagnosed until later in life as the symptoms change as the person ages.

Noonan syndrome can range from being very mild to severe and potentially life-threatening. Early diagnosis is key to ensure any complications, especially affecting the heart, can be monitored and treated.

Hear advice from other parents whose children are also short in stature, compared with others their age.

What causes Noonan syndrome?

Noonan syndrome is caused by a genetic mutation, which is a change in your gene that can be caused by all kind of factors and often happens spontaneously. The exact gene the fault lies in varies; this determines which symptoms the person with Noonan syndrome experiences.

Half of the people with Noonan syndrome (50%) have a mutation in the PTPN11 gene. Noonan syndrome is associated with physical symptoms and signs such as a type of heart defect called pulmonary valve stenosis, as well as a short stature and easy bruising.

Some cases of Noonan syndrome arise sporadically. They are caused by a genetic mutation that has arisen randomly. The mutation occurs for the first time in the child with Noonan syndrome and is not found in either parent.

In other cases, Noonan syndrome is inherited in an autosomal dominant manner. This means that people with Noonan syndrome only need to have one copy of the faulty gene to be affected. When a person with Noonan syndrome has a child, there is a 50% chance that their child will also have Noonan syndrome.

What are the symptoms of Noonan syndrome?

Noonan syndrome is variable in how it affects different people. Most people with Noonan syndrome will have these three symptoms:

  • Characteristic facial features which are most obvious in early childhood and become less prominent in adults
  • Congenital heart disease which is present from birth
  • Reduced growth

Facial features

The characteristic facial features of Noonan syndrome are:

  • Triangular face shape (broad forehead that narrows towards the chin)
  • Drooping eyelids
  • Widely spaced eyes
  • Short nose with a broad tip
  • Low-set ears that are rotated back
  • Prominent Cupid’s bow
  • Short neck
  • Low hairline
  • Webbed neck (in babies)

Congenital heart disease

70–80% of people with Noonan syndrome have some form of heart defect including:

  • Pulmonary valve stenosis (narrowing of valve that controls blood flow from the heart to the lungs)
  • Hypertrophic cardiomyopathy (abnormal thickening of heart muscle)
  • Septal defects (the heart wall that separates different chambers of the heart fails to close, leaving a hole)


Infants with Noonan syndrome are usually within the normal range for size for their age, although they may be at the smaller end of the scale.

Children with Noonan syndrome typically begin puberty a couple of years late, averaging at age 13 across both sexes. The growth spurt that occurs during puberty isn’t as large as for other teenagers and takes place later than usual. However, as bone ageing is also delayed, some teenagers catch up on growth in their late teens and can reach normal adult height.

If your child is short in stature, keeping track of their growth can help identify if there is a problem early on. Compare your child’s measurements to the national average to see if they are within a healthy range.

Calculate your child’s growth

It is important to keep track of your child’s growth in order to identify if there is a problem early on. We recommend measuring your child every 6 months, which is now easier, with our simple to use growth calculator.

What complications are associated with Noonan syndrome?

People with Noonan syndrome are more likely to experience certain medical issues including:

  • Hashimoto’s thyroiditis
  • Scoliosis
  • Chest deformities
  • Increased bruising or bleeding
  • Difficulties with language and communication
  • Dental problems
  • Eye problems including squint, lazy eye and cataracts
  • Decreased muscle tone
  • Undescended testicles
  • Increased risk of blood cancers and solid tumours

How is Noonan syndrome diagnosed?

Despite advances in molecular testing, Noonan syndrome is diagnosed primarily on the presence of certain clinical characteristics and symptoms. However, there is overlap in the symptoms of Noonan syndrome and other conditions and people with Noonan syndrome can vary in exactly which symptoms they have.

If your doctor suspects your child to have Noonan syndrome, they will likely refer them for genetic testing. The genetic testing involves taking a sample of your child’s blood, which will be tested for all known mutations associated with Noonan syndrome. The genetic mutation that causes Noonan syndrome is yet to be identified in 20–30% of people with the syndrome. Therefore, a negative genetic test result does not rule out a diagnosis of Noonan syndrome.

If your child has a positive genetic test, your primary care physician should regularly check for any complications known to be associated with their genetic mutation and refer them to a specialist if needed.

It is important you speak to your doctor if you have any concerns about your child’s height. Use this helpful guide on what questions to ask and what to expect from your visit.


Is Noonan syndrome more common in males or females?

Noonan syndrome affects males and females equally, with roughly the same number of births recorded.

Can Noonan syndrome be detected before birth?

Noonan syndrome can be detected prior to birth. Screening is recommended for parents who show signs of Noonan syndrome or who have people with Noonan syndrome in their close family.

Ultrasound, foetal echocardiogram (an ultrasound used to look at the baby’s heart) and DNA testing can all be used to identify whether the baby has Noonan syndrome.

How does Noonan syndrome affect learning?

Most people with Noonan syndrome are within the normal range for intelligence. People with Noonan syndrome are more likely to have difficulties with reading and spelling than the general population. Some may also struggle with tasks that require memory recall.