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Noonan Syndrome: Definition, Symptoms & Facts

Instructor: Artem Cheprasov
This lesson goes over a condition known as Noonan Syndrome. You'll learn why it occurs, its frequency, and many of the major signs and symptoms of this condition.

What Is Noonan Syndrome?

Noonan syndrome is a genetic disorder that involves numerous physical and mental abnormalities. This disorder is named after a pediatric cardiologist who characterized the disorder. Her name is Jacqueline Anne Noonan.

In this lesson, you will learn more about the cause, signs, symptoms, and facts of this disorder.

The Cause of Noonan Syndrome.

As you just learned, Noonan syndrome is a genetic disorder. In other words, it's not caused by some contagious or infectious agent such as a bacterium or virus. People are born with this disorder as a result of some sort of abnormality in our genetic code. Like a problem in a computer code can cause the computer to malfunction, a mutation in our genetic code can cause the abnormalities seen in Noonan syndrome.

Specifically, the mutation occurs in one of four autosomal dominant genes. This means that the affected person needs to only have one copy of the defective gene in order to be affected by Noonan syndrome. Mutations in one of four genes can cause Noonan syndrome:

  • PTPN11
  • SOS1
  • RAF1
  • KRAS

This disorder can also occur as a result of a spontaneous (random) mutation in one of these genes. In other words, the parents do not carry the defective gene.

Signs, Symptoms & Stats

Noonan syndrome is, well, a syndrome. A syndrome is a collection of signs and symptoms stemming from an abnormal process. Noonan syndrome occurs in roughly 1 in 1,750 people.

Some of the most characteristic signs and symptoms of Noonan syndrome include:

  • Hypertelorism, which refers to an abnormally large distance between (namely paired) organs or body parts. In the case of Noonan syndrome, this mainly means widely spaced eyes.
  • Downward slanting eyes
  • A short, webbed neck
  • Congenital heart disease in the vast majority of patients. In other words, a heart defect is present immediately at birth. This may include pulmonary valve stenosis, which is the narrowing of a valve that allows for blood to flow from the heart and into the lungs.
  • Short stature in 50%-80% of all individuals affected with this disorder. This results in an average height of 5 feet for women and 5 feet 5 inches in males.
  • Chest deformity such as pectus excavatum, which is a sunken chest, or pectus carinatum, which is a protruding chest.

A child with Noonan syndrome
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Additionally:

  • Around 25% of people with Noonan syndrome are intellectually disabled.
  • Upwards of 50% of individuals with Noonan syndrome have bleeding diathesis. This, in short, is a term for the fact that a person has an unusual tendency to bleed in excess.
  • Up to 95% of people will have eye problems, such as strabismus. Strabismus is a condition where the eyes point in different directions.
  • Males are likely to have cryptorchidism, which refers to one or more undescended testicles. This can lead to an increased risk of testicular cancer or infertility later in life.
  • External ear abnormalities such as low set ears and/or ears that are rotated backwards.
  • Lymphedema, which refers to fluid buildup in the body's tissues. This can lead to puffy hands and puffy feet.
  • Scoliosis, a side to side curvature of the spine.

Lesson Summary

Noonan syndrome is an autosomal dominant genetic disorder cause by a mutation in one of four genes:

  • PTPN11
  • SOS1
  • RAF1
  • KRAS

It occurs in about 1 in 1,750 people. Some of its signs and symptoms include:

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