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Noonan syndrome is a genetic disorder that may present with mildly unusual facial features, short height, congenital heart disease, bleeding problems, and skeletal malformations. Facial features include widely spaced eyes, light-colored eyes, low-set ears, a short neck, and a small lower jaw. Heart problems may include pulmonary valve stenosis. The breast bone may either protrude or be sunken, while the spine may be abnormally curved. Intelligence in the syndrome is often normal. Complications of NS can include leukemia.
A number of genetic mutations can result in Noonan syndrome. The condition may be inherited from a person's parents as an autosomal dominant condition or occur as a new mutation. Noonan syndrome is a type of RASopathy, the underlying mechanism for which involves overactivation within the RAS/MAPK cell signaling pathway. The diagnosis may be suspected based on symptoms, medical imaging, and blood tests. Confirmation may be achieved with genetic testing.
No cure for NS is known. Treatment is based on the symptoms and underlying problems, and extra support in school may be required. Growth hormone therapy during childhood can increase an affected person's final height. Long-term outcomes typically depend on the severity of heart problems.
An estimated 1 in 1000 people are mildly affected by NS, while about 1 in 2,000 have a more severe form of the condition. Males appear to be affected more often than females. The condition was first described in 1883 and was named after American pediatric cardiologist Jacqueline Noonan, who described further cases in 1963.