What Is Noonan Syndrome?
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Noonan Syndrome - Causes, Symptoms, Diagnosis, and Treatment

Published on Dec 12, 2022 and last reviewed on Aug 29, 2023   -  6 min read


Noonan syndrome is a genetic disorder that affects normal development in various parts of the body. Read this article to know more about it.


Noonan syndrome is a disorder that affects many parts of the body. It can be present from birth (congenital condition) and passed down within families (inherited). The characteristic features of this syndrome include various signs and symptoms such as unusual facial features, short stature, heart disorders, bleeding problems, and skeletal malformations. The disease can be present before birth, and some milder cases may not be diagnosed until a child gets older.

What Is Noonan Syndrome?

Noonan syndrome (NS) is also known as female pseudo-Turner syndrome or male Turner syndrome. It is a rare genetic disorder caused by a genetic mutation. It has many physical and developmental symptoms that usually start at birth. The condition has the tendency to appear in one of every 1000 to 2500 people and is more common in people with a family history of Noonan syndrome.

What Causes Noonan Syndrome?

Noonan syndrome is caused by a defect in one of the many genes. There have been eight different genes reported to be involved in this syndrome. And there has been no evidence of the cause of this defect or mutation.

Sometimes, the mutated gene is inherited or transferred from one of the parents. And the parent with the mutated gene may or may not show features of this disease. However, only one parent needs to carry the defective gene to pass it on, and every child they have will have a 50 % chance of being born with this condition.

In other cases where the condition is not inherited from the parents and the disease is caused by some new genetic mutation, the chances of Noonan syndrome are very low in the next child.

What Are the Symptoms of Noonan Syndrome?

The signs and symptoms involved in Noonan syndrome vary greatly, as it affects several parts of the body. In addition, the symptoms can range from mild to severe, and the feature depends upon the respective gene mutation.

Some of the signs or symptoms involved in this disorder are:

Facial Features:

Facial features are one of the leading clinical criteria that help diagnose Noonan syndrome. These features are more prominent in young children and infants, and the features start to disappear with age.

Some of the features involved are as follows:

Heart Disease:

Growth Issues:

Noonan syndrome causes various growth issues, which may include:

  • Growth is slow or retarded.

  • Growth hormone levels will not be sufficient.

  • Delayed puberty.

  • By adulthood, the patient may have average height but short stature.

Musculoskeletal Issues:

  • Unusually shaped chest, such as the sunken sternum (pectus excavatum) or raised sternum (pectus carinatum).

  • Wide-set nipples.

  • Short neck with additional folds of skin (webbed neck).

  • Deformities of the spine.

Learning Disabilities:

  • Mental, emotional, and behavioral issues.

  • Hearing and vision defects.

  • Learning disabilities and intellectual disability.

Eye Conditions:

Some of the common signs of Noonan syndrome include eyes and eyelids.

  • Problems with the eye muscles.

  • Refractive problems, such as astigmatism (a defect in the curvature of the eye), nearsightedness (myopia), or farsightedness (hyperopia).

  • Uncontrolled or fast movement of the eyeballs (nystagmus).

  • Cataracts (cloudy eye lens).

Hearing Problems:

Noonan syndrome can cause hearing defects due to nerve issues and structural abnormalities.

Bleeding Issues:

Noonan syndrome can cause clotting defects, leading to excessive bleeding and bruising.

Genital and Kidney Conditions:

Males have more problems with their genital and kidney, which are:

  • Testicles: Cryptorchidism or undescended testicles are common in males in which one or both testes fail to descend from the abdomen into the scrotum.

  • Puberty: Puberty can get delayed in both boys and girls.

  • Fertility: Males usually have fertility issues due to undescended testicles.

  • Kidneys: Kidney problems are mild and occur in only a few people.

Skin Conditions:

People with Noonan syndrome can develop skin conditions such as changes in the color and texture of the skin.

How Is Noonan Syndrome Diagnosed?

Noonan syndrome can be diagnosed by conducting a physical examination. Additionally, some other tests are also undertaken, such as -

  • Platelet Count Test - This test measures the number of platelets in the blood to check for any bleeding disorder (normal count - 150,000 to 450,000 platelets per microliter of blood).

  • Blood Clotting Factor Test - This test checks for any clotting disorder by measuring the time the blood takes to clot.

  • ECG - Electrocardiogram (ECG or EKG) records the electrical signal from the heart to evaluate any heart conditions.

  • Chest X-ray or Echocardiogram - Chest radiograph or ultrasound of the chest to see hearts and nearby blood vessels.

  • Hearing Tests - These are done to check the hearing senses of the patient.

  • Growth Hormone Levels - The growth hormone levels can be assessed by a blood test to check for any growth-related disorders.

  • Genetic Testing - This can help diagnose this syndrome at an early stage.

What Is the Treatment of Noonan Syndrome?

Treatment for Noonan syndrome depends upon the type and severity of symptoms as this condition involves various body structure disorders which require a coordinated team approach.

Recommended approaches may include:

  • Heart Treatment: Heart diseases can be treated medically however, valvular conditions may require surgical treatment

  • Treating Low Growth Rate: Regular blood tests are required to evaluate nutrition, and height should be measured three times a year until three years of age. And if the growth seems to be insufficient, growth therapy is the option.

  • Vision and Hearing Treatments: Most eye issues can be treated using correction glasses, and surgery is required in cases like cataracts (clouding of the clear eye lens). In addition, an eye examination should be done every two years, and hearing tests should be done annually.

  • Treatment for Bleeding and Bruising: If the patient has a bleeding disorder, they should avoid Aspirin, and doctors may prescribe drugs to help the blood clot.

  • Treatment for Genital Problems: In cases with undescended testicles, if one or both testicles have not been in the proper position within the first few months, then surgery is required.

How to Prevent Noonan Syndrome?

As this syndrome is related to genetic mutations, it can happen spontaneously, and there is no proper way to prevent it. However, if a person has a family history of Noonan syndrome, they should consult the doctor and take advice as this can still be detected using molecular genetic testing.


Noonan syndrome is a highly complex condition as various bodily structures get involved. However, with treatment, most people can manage to lead a healthy life with it. In this syndrome, early diagnosis and treatment are the only way to manage symptoms and prevent complications further in life.

Last reviewed at:
29 Aug 2023  -  6 min read




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