Noonan syndrome

Definition of Noonan syndrome

Noonan syndrome is a genetic disorder that causes abnormal development of multiple parts of the body. It used to be called Turner-like syndrome because certain symptoms (webbing of neck and abnormally shaped chest) resembled those seen in .

Causes, incidence, and risk factors

Defects in four genes (KRAS, PTPN11, RAF1, SOS1) can cause Noonan syndrome. About half of those affected by Noonan syndrome have a PTPN11 mutation. Persons with a defect in the KRAS gene have a more severe form of Noonan syndrome. Those with defects in the RAF1 gene tend to have a particular heart problem (hypertrophic cardiomyopathy). Problems with these genes cause certain proteins involved in growth and development to become overactive.

Signs and tests

Examination may show an extra fold of skin above the eyes near the nose (epicanthal folds) and arms that may be held at an unusual angle.


There is no single treatment for Noonan syndrome. Treatment focuses on the individual symptoms. Growth hormone has been used successfully to treat short stature in some persons with Noonan syndrome.

Expectations (prognosis)

The expected outcome depends on the extent and severity of symptoms. Patients can lead normal lives.


Chad Haldeman-Englert, MD, Wake Forest University School of Medicine, Department of Pediatrics, Section on Medical Genetics, Winston-Salem, NC. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc. – 8/26/2009

Pectus excavatum

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