Noonan Syndrome: Causes, Symptoms, Diagnosis, and Treatments

Noonan syndrome

Noonan syndrome is a genetic disorder that prevents normal development in various parts of the body. A person can be affected by Noonan syndrome in a variety of ways. These include unusual facial features, short stature, heart defects, other physical problems, and possible developmental delays.


Noonan syndrome is caused by a genetic mutation and is acquired when a child inherits one copy of an affected gene from a parent (dominant inheritance). It can also occur as a spontaneous mutation, meaning there is no family history involved.


Signs and symptoms of Noonan syndrome vary greatly between individuals and can range from mild to severe. The characteristics may be related to the specific gene that contains the mutation.

Facial appearance is one of the key clinical features leading to a diagnosis of Noonan syndrome. These features may be more pronounced in infants and young children but change with age. In adulthood, these distinct features become more subtle.

Features may include the following:

  • The eyes are set wide apart and slanted downwards with droopy lids. The irises are blue or green.
  • The ears are set low and rolled back.
  • The nose is depressed at the top, with a broad base and bulbous tip.
  • The mouth has a deep groove between the nose and mouth and broad peaks in the upper lip. The crease running from the edge of the nose to the corner of the mouth becomes deeply furrowed with age. The teeth may be crooked, the inner palate may be highly arched, and the lower jaw may be small.
  • Facial features may appear coarse, but appear sharper with age. The face may appear saggy and expressionless.
  • The head may appear large with a prominent forehead and low hairline at the back of the head.
  • Skin may appear thin and transparent with age.

Between 50 and 70 percent of individuals with Noonan syndrome have short stature. At birth, they are usually of normal length and weight, but growth slows over time. Abnormal levels of growth hormone, a protein needed for normal growth of bone and body tissue, can contribute to slow growth.

Individuals with Noonan syndrome often have a sunken chest (pectus excavatum) or a protruding chest (pectus carinatum). Some affected people may also have an abnormal side-to-side curvature of the spine (scoliosis).

Most people with Noonan syndrome have some form of critical congenital heart disease. The most common heart defect in these individuals is a narrowing of the valve that controls blood flow from the heart to the lungs (pulmonic valve stenosis). Some have hypertrophic cardiomyopathy, which enlarges and weakens the heart muscle.

A variety of bleeding disorders have been associated with Noonan syndrome. Some affected individuals experience excessive bruising, nosebleeds, or prolonged bleeding following injury or surgery. Rarely, women with Noonan syndrome who have a bleeding disorder have excessive bleeding during menstruation (menorrhagia) or childbirth.

Adolescent males with Noonan syndrome typically experience delayed puberty. They go through puberty starting around the age of 13 or 14 and have a reduced pubertal growth spurt which results in a short stature. Most males with Noonan syndrome have undescended testicles (cryptorchidism), which can contribute to infertility (the inability to bear a child) later in life. Females with Noonan syndrome may have delayed puberty, but most have normal puberty and fertility.

Noonan syndrome can cause a variety of other signs and symptoms. Most children diagnosed with Noonan syndrome have normal intelligence, but some have special educational needs and some have intellectual disabilities. Some affected individuals have vision or hearing problems. Affected infants may have feeding problems, which usually improve by age 1 or 2 years. Newborns with Noonan syndrome may be born with swollen hands and feet caused by a buildup of fluid (lymphedema), which may go away on its own. Older individuals may also develop lymphedema, usually in the ankles and lower legs.

Some people with Noonan syndrome develop cancer, particularly those involving blood-forming cells (leukemia). It has been estimated that children with Noonan syndrome have an eight times greater risk of developing leukemia or other cancers than their age-matched peers.


In some cases, Noonan syndrome may be suspected before birth (prenatal) based on the results of fetal ultrasound, a specialized imaging techniquein which sound waves are used to create an image of the developing fetus. A diagnosis of Noonan syndrome may be considered because of an abnormal triple maternal serum screening, detection of excessive amniotic fluid surrounding the fetus within the amniotic sac (polyhydramnios), presence of an abnormal cystic swelling consisting of lymphatic vessels dilated in the neck area (polyhydramnios). hygroma), a structural cardiac difference, other fetal abnormalities, and confirmation of a normal chromosome composition (karyotype). However, in many cases, Noonan syndrome is diagnosed at birth or in early childhood based on a thorough clinical evaluation, identification of characteristic physical signs, and a series of specialized tests.of cell-free fetal DNA .

It is important to note that, in some cases, individuals who have only minor and subtle features associated with Noonan syndrome may not receive a diagnosis. Physicians who specialize in the diagnosis and treatment of heart abnormalities (cardiologists) should suspect the possibility of Noonan syndrome in any individual with congenital pulmonary valve stenosis.

Risk factors

A parent with Noonan syndrome has a 50% chance (one in two chance) of passing the defective gene to their child. The child who inherits the defective gene may have fewer or more symptoms than the affected parent.


Noonan syndrome occurs in about 1 in 1,000 to 2,500 people.


There is currently no single treatment for Noonan syndrome, but many aspects of the condition can often be successfully managed.

For example, serious heart defects may need to be repaired with surgery, and growth hormone drugs may be used to treat short stature in some people with Noonan syndrome.

Katherine Johnson, M.D., is a board-certified obstetrician-gynecologist with clinical expertise in general obstetrics and gynecology, family planning, women’s health, and gynecology.

She is affiliated with the Obstetrics and Gynecology division at an undisclosed healthcare institution and the online platform,

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