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Noonan Syndrome

Noonan syndrome facts*

*Noonan syndrome facts medical author: Benjamin Wedro, MD, FACEP, FAAEM

  • Noonan syndrome is a genetic disorder that may cause short stature, distinctive facial features and heart abnormalities.
  • Aside from face and heart abnormalities, there may be associated bleeding abnormalities, scoliosis, infertility in males, lymphedema, and intellectual disability.
  • It is inherited as an autosomal dominant disease, meaning that the abnormal gene is on a non-sex chromosome and requires just one of two inherited genes to be abnormal.
  • The syndrome may also occur by a spontaneous mutation of the gene involved.
  • Since it is a genetic disease, there is no cure.

What is Noonan syndrome?

Noonan syndrome is a condition that affects many areas of the body. It is characterized by mildly unusual facial characteristics, short stature, heart defects, bleeding problems, skeletal malformations, and many other signs and symptoms.

What are the signs and symptoms of Noonan syndrome?

People with Noonan syndrome have distinctive facial features such as a deep groove in the area between the nose and mouth (philtrum), widely spaced eyes that are usually pale blue or blue-green in color, and low-set ears that are rotated backward. Affected individuals may have a high arch in the roof of the mouth (high-arched palate), poor alignment of the teeth, and a small lower jaw (micrognathia). Many children with Noonan syndrome have a short neck and both children and adults may have excess neck skin (also called webbing) and a low hairline at the back of the neck.

Approximately 50 to 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 may contribute to the slow growth.

Individuals with Noonan syndrome often have either 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 a heart defect. The most common heart defect is a narrowing of the valve that controls blood flow from the heart to the lungs (pulmonary valve stenosis). Some affected individuals have hypertrophic cardiomyopathy, which is a thickening of the heart muscle that forces the heart to work harder to pump blood.

A variety of bleeding disorders have been associated with Noonan syndrome. Some people may have excessive bruising, nosebleeds, or prolonged bleeding following injury or surgery. Women with a bleeding disorder typically have excessive bleeding during menstruation (menorrhagia) or childbirth.

Adolescent males with Noonan syndrome typically experience delayed puberty. Affected individuals go through puberty starting at age 13 or 14 and have a reduced pubertal growth spurt. Most males with Noonan syndrome have undescended testicles (cryptorchidism), which may be related to delayed puberty or to infertility (inability to father a child) later in life. Females with Noonan syndrome typically 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 a small percentage has special educational needs, and some have intellectual disability. Some affected individuals have vision or hearing problems. Infants with Noonan syndrome may be born with puffy hands and feet caused by a buildup of fluid (lymphedema), which can go away on its own. Affected infants may also have feeding problems, which typically get better by age 1 or 2. Older individuals can also develop lymphedema, usually in the ankles and lower legs.


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