Noonan syndrome (2024)

Noonan syndrome is a genetic condition that usually includes heart anomalies and characteristic facial features. About one third of affected children have mild intellectual disability. Noonan syndrome varies from relatively mild to severe. The physical characteristics are not always obvious and can be hard to identify in individuals with more subtle traits.

Estimates vary, but it is thought that between one in 1,000 to one in 5,000 children have Noonan syndrome, with males and females equally affected. Genetic changes on several genes are known to cause Noonan syndrome, but the diagnosis is usually established on the basis of clinical features.

Currently there is no cure, but symptoms of Noonan syndrome can be medically managed. Your child’s health care team will coordinate various management strategies for different symptoms. These can include cardiac monitoring for heart irregularities, medication for blood clotting, and speech and educational interventions for any learning difficulties they may experience.

Effects of Noonan syndrome

Parts of the body typically affected by Noonan syndrome include:

heart
facial features
musculoskeletal system
kidneys, spleen, genitals and liver.

Associated heart conditions

About 65 per cent of children with Noonan syndrome have heart anomalies. The most common include:

Characteristic facial features

Some facial features are characteristic of Noonan syndrome. How these features are expressed in children with Noonan syndrome varies from one child to the next and can change with age. Characteristics may include:

heavy or hooded eyelids that may interfere with vision (ptosis)
downward sloping eyes with an extra fold of skin at each inner corner
widely spaced eyes (hypertelorism) with a flattened bridge of the nose
brilliant blue or blue-green eyes
strongly arched (diamond-shaped) eyebrows
low-set ears, tilted back so that the lobes point forward more than usual
low hairline at the neck
coarse and curly hair
short neck with extra skin folds or ‘webbing’ at the back of the neck – this makes the neck look wider when viewed from behind.

Associated musculoskeletal conditions

Some possible anomalies of the musculoskeletal system include:

short stature – although birth weight is usually average, children with Noonan syndrome are frequently shorter than expected for their age. As adults, people with Noonan syndrome are often short – men average 165 cm (5’ 5") and women 152 cm (5’) in height
low muscle tone and impaired coordination
unusually shaped breastbone (sternum) – may be sunken or raised
curvature of the spine (scoliosis).

Associated kidney, spleen, genital and liver conditions

Noonan syndrome can also affect the kidneys, spleen, genitalia and liver:

Puberty can be delayed in both males and females.
Females are normally fertile, however up to 80 per cent of males can have reduced fertility due to deficient sperm production, undescended testicl*s or testicular dysfunction.
Approximately 25 to 50 per cent of people with Noonan syndrome can develop an enlarged liver or spleen.
Less than 10 per cent of people with Noonan syndrome will develop mild kidney problems.

Learning and language issues with Noonan syndrome

Up to 35 per cent of people with Noonan syndrome will have a mild intellectual disability, but most people will be unaffected.

People who experience intellectual disability with Noonan syndrome may also experience developmental delays with their speech, language and coordination. They may also exhibit some mild emotional and behavioural issues.

Other issues associated with Noonan syndrome

Depending on the severity, other issues experienced by people with Noonan syndrome may include:

Cause of Noonan syndrome

Noonan syndrome is a genetic condition caused by a change in one of at least seven different genes. Genetic testing has shown that a change in the PTPN11 gene causes Noonan syndrome in about 50 per cent of affected people.

It was once believed that most cases of Noonan syndrome were sporadic, which means the child’s gene spontaneously changed. However, researchers now suspect that Noonan syndrome is inherited in up to 75 per cent of cases.

The pattern of inheritance is autosomal dominant, which means that the gene (and the condition) can be transmitted from parent to child. Each child of a parent who carries the gene has a 50 per cent chance of inheriting the gene and developing the condition.

Diagnosis of Noonan syndrome

Diagnosis is generally made by noting the presence of typical Noonan syndrome features and ruling out other possible causes, such as fetal alcohol spectrum disorder, neurofibromatosis type 1 (also known as Von Recklinghausen’s disease, or NF1) and Turner’s syndrome.

Genetic testing is available for Noonan syndrome and options can be discussed with your health professional.

Treatment for Noonan syndrome

There is currently no cure for Noonan syndrome. Treatment and condition management aims to ease some of the associated issues. If your child has been diagnosed with Noonan syndrome their treatment may include:

for a mild heart irregularity, it may be enough to carefully monitor your child on an outpatient basis
surgical correction of any severe heart structural anomalies
if feeding is a problem, your baby may be fed by nasogastric tube (a tube threaded into the nose, down the oesophagus and into the stomach)
prescription glasses – to correct short-sightedness
regular injections of growth hormone – to help your child achieve a height closer to that typical for their age
surgical correction of undescended testicl*s (orchidopexy)
anticonvulsant medication – if your child experiences seizures
speech therapy
special education – this is necessary for about 10 per cent of children with Noonan syndrome
behaviour management – if appropriate
treatment to manage mild blood-clotting problems
dental and orthodontic treatment
if glue ear is a problem, it can be managed with an operation to insert drainage tubes (grommets).

Genetic counselling and Noonan syndrome

If you, your child or another family member have been diagnosed with Noonan syndrome, or if Noonan syndrome runs in your family, it can be helpful to speak to a genetic counsellor.

Genetic counsellors are health professionals qualified in both counselling and genetics. As well as providing emotional support, they can help you to understand a condition and what causes it, how it is inherited, and what a diagnosis means for your or your child’s health and development for the future. Genetic counsellors are trained provide information and support that is sensitive to your family circ*mstances, culture and beliefs.

If a Noonan syndrome runs in your family, a genetic counsellor can explain what genetic testing options are available to you and other family members. You may choose to visit a genetic counsellor if you are planning a family, to find out your risk of passing that condition on to your child, or to arrange for prenatal tests.

The Noonan Syndrome Awareness Association website provides information about the condition as well as Noonan syndrome research, resources and support.

Where to get help

Your GP (doctor)
Victorian Clinical Genetics Services (VCGS), Royal Children’s Hospital Tel. 1300 118 247
Genetic Support Network of Victoria Tel. (03) 8341 6315
Noonan Syndrome Awareness Association