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Genetic

Noonan syndrome

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Definition

Noonan syndrome is a disease that can be passed down through families (inherited). It causes abnormal development in many parts of the body. Noonan syndrome used to be called Turner-like syndrome.

Causes, incidence, and risk factors

Noonan syndrome is linked to defects in several genes. Problems with the genes cause certain proteins involved in growth and development to become overactive.

Noonan syndrome is an autosomal dominant condition. This means only one parent has to pass down the faulty gene for the baby to have the syndrome. However, some cases may not be inherited.

Symptoms

  • Delayed puberty
  • Down-slanting or wide-set eyes
  • Hearing loss (varies)
  • Low-set or abnormally shaped ears
  • Mild mental retardation (only in about 25% of cases)
  • Sagging eyelids (ptosis)
  • Short stature
  • Small penis
  • Undescended testicles
  • Unusual chest shape (usually a sunken chest called pectus excavatum)
  • Webbed and short-appearing neck

Signs and tests

The health care provider will perform a physical exam. This may show signs of congenital heart disease (especially pulmonary stenosis, occasionally ASD).

Tests depend on the symptoms, but may include:

  • Platelet count
  • Blood clotting factor test
  • EKG, chest x-ray, or echocardiogram
  • Hearing tests

Genetic testing can help diagnose this syndrome.

Treatment

There is no specific treatment. Your doctor will suggest treatment to relieve or manage symptoms. Growth hormone has been used successfully to treat short stature in some persons with Noonan syndrome.

Support Groups

The Noonan Syndrome Support Group, Inc. -- www.noonansyndrome.org

Complications

  • Buildup of fluid in tissues of body (lymphedema, cystic hygroma)
  • Failure to thrive in infants
  • Low self-esteem
  • Male infertility in those with both testes undescended
  • Problems with the structure of the heart
  • Short stature
  • Social difficulties related to physical symptoms

Calling your health care provider

This condition may be detected on early infant exams. Evaluation by an experienced geneticist is often needed to diagnose Noonan syndrome.

Prevention

Couples with a family history of Noonan syndrome may want to consider genetic counseling before having children.

References

Rapaport R. Hypofunction of the ovaries. In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics. 18th ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 587.

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