Noonan syndrome - Characteristics of Noonan syndrome

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

The three most common characteristics of Noonan syndrome are:

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

These are discussed in more detail below.

Unusual features

Unless your child is only mildly affected by Noonan's syndrome, facial features associated with the condition usually become apparent following birth.

They include:

• a broad forehead
• drooping eyelids (ptosis)
• a wider than usual distance between the eyes
• 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

As your child gets older, their face is likely to become more triangular. Their lips may also thicken and the folds of skin that run from each side of the nose to the corners of the mouth may become more noticeable.

By the time your child reaches their teenage years, their eyes will become less prominent and their neck should become longer. However, the lengthening of the neck can reveal extensive folds of skin (skin webbing). By adulthood, the eyelids will look thick and hooded.

Children with Noonan syndrome also have abnormalities that affect the bones of the chest such as:

• a chest that sticks out or sinks in
• an usually wide chest with a large distance between the nipples

Short stature

Children born with Noonan syndrome are usually a normal length at birth. Their short stature usually becomes apparent when they are around two years old.

After this time, they don't grow as quickly as children of the same age. Puberty (when a child begins to mature sexually and physically) is typically delayed for up to two years and the expected growth spurt that happens during puberty is either reduced or doesn’t happen at all.

This is sometimes treated with a type of medication, known as human growth hormone. Left untreated, the average adult height for men with Noonan syndrome is 162.5cm (5ft 3in) and for women is 153cm (5ft).

Read more information about restricted growth.

Congenital heart disease

An estimated 80-90% of children with Noonan syndrome will have some form of congenital heart disease. This may be one of the following:

Pulmonary stenosis

Pulmonary stenosis is the most common type of congenital heart disease, affecting around half of all children with Noonan syndrome. It occurs when the pulmonary valve (the valve that helps control the flow of blood away from the heart and into the lungs) is unusually narrow. This means that the heart has to work much harder to pump blood into the lungs. In many cases there will be no symptoms and no treatment is required, but if the obstruction is severe it can be corrected by surgery (see below).

Hypertrophic cardiomyopathy (HCM)

Hypertrophic cardiomyopathy (HCM) is the second most common type of congenital heart disease in children with Noonan syndrome, affecting an estimated 20-30% of children.

In cases of HCM, the muscles of the heart are much larger than they should be. This can place strain on the heart and cause symptoms such as breathlessness.

HCM in Noonan syndrome can cause heart failure in infancy. However, HCM usually improves with age.

Septal defects

A septal defect is a hole between two of the chambers of the heart, often referred to as having a ‘hole in the heart’. The hole can be between the upper chambers (atrial septal defects) or the lower chambers (ventricular septal defects).

Read more about congenital heart disease.

Other characteristics

Other, less common characteristics of Noonan syndrome are briefly described below.

Learning difficulties

Some children with Noonan syndrome will have learning difficulties, which are usually mild.

To put this in context, the average intelligence quotient (IQ) score is 100. The average IQ of children with Noonan syndrome affected by a learning difficulty is around 70.

Increased bruising or bleeding

Around 50% of children with Noonan syndrome have a defect that means that their blood does not clot properly. This makes their skin more vulnerable to bruising and they may bleed excessively from cuts.

If your child is affected and needs surgery or dental work, they will need to be observed for longer than usual afterwards, in case of bleeding. 

Eye conditions

Around half of children with Noonan syndrome will have one or more eye conditions, including:

• a squint, where one eye does not look straight ahead but turns inwards, outwards, upwards or downwards
• astigmatism, where the cornea (the transparent layer at the front of the eye) is not a perfectly shaped curve, causing blurred vision
• lazy eye, where one eye is less able to focus than the other eye, leading to an increasing reliance on the more effective eye

Lymphatic problems

Children with Noonan syndrome have problems with their lymphatic system. Most commonly this causes a build-up of lymph fluid in their feet resulting in severe swelling. This is known as lymphoedema.  

Hypotonia

Hypotonia is decreased muscle tone. Most children with Noonan syndrome will have a degree of hypotonia, which may mean it takes them longer to reach developmental milestones during early childhood.

Hearing loss

Children with Noonan syndrome may experience temporary bouts of hearing loss. This is caused by a build-up of fluid inside the middle ear, which is known as Otitis media.

Infertility and undescended testicles

In around 60% of boys with Noonan syndrome, either one or both of their testes fails to drop into the scrotum (the bag that holds the testicles). It is important that this is corrected through surgery at an early age, to avoid reduced fertility in later life. Many older males who have not had early corrective surgery may have a reduced sperm count.

Read more about undescended testicles and infertility.

Feeding problems

Many babies with Noonan syndrome have feeding problems such as:

• sucking problems, due to weak muscles in the mouth and sometimes a high-arched palate
• a weak chewing action that can mean mealtimes take longer than expected
• projectile vomiting during or after meals

These sorts of feeding problems can cause babies to gain weight at a lower than expected rate. This is often referred to as ‘failure to thrive’. However, feeding problems usually resolve once a child reaches two years of age.

Behavioural difficulties

Children with Noonan syndrome may show difficult behaviour, although it is not usually severe enough to need specialist help. Common types of difficult behaviour include:

• being a very fussy eater, for example, some children will refuse to eat certain flavours or textures of food
• being very stubborn or irritable at certain times
• repeating sounds and words said by other people

Problems with bones and joints

Some children with Noonan syndrome will develop problems that affect normal development of bones and joints (orthopaedic problems). For example:

• Joint hypermobility, where joints have an unusually wide range of movement. This affects around half of children with Noonan syndrome.
• Abnormally curved spine (scoliosis). This affects a small number of children with Noonan syndrome.