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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 Turner syndrome.
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.
Noonan syndrome is inherited, which means it is passed down through families. It is an autosomal dominant condition. This means that only one parent has to provide the faulty gene for the baby to have the syndrome. However, the fact that some children do not have a parent with Noonan syndrome likely means that some cases are not inherited.
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.
Blood tests to look at platelet count and blood factors may reveal signs of a bleeding tendency.
Specific tests depend on what the symptoms are. For example, if there are signs of heart disease, an EKG, chest x-ray, or echocardiogram may be recommended. Hearing tests are recommended for those who have signs of decreased hearing.
Genetic testing can identify the mutations in the four genes which cause Noonan syndrome.
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.
The Noonan Syndrome Support Group, Inc. -- www.noonansyndrome.org
The expected outcome depends on the extent and severity of symptoms. Patients can lead normal lives.
This condition may be detected on early infant exams. Evaluation by an experienced geneticist is often needed to diagnose Noonan syndrome.
Couples with a family history of Noonan syndrome may want to consider genetic counseling before having children.
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.