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 the KRAS and PTPN11 genes 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 severe or atypical form of Noonan syndrome. 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. However, the fact that some children do not have a parent with Noonan syndrome likely reflects that some cases may occur due to new mutation in a gene.

The disease occurs in approximately 1 in 1,000 to 2,500 children.

• 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

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

There may be signs of congenital heart disease (especially pulmonary stenosis, occasionally ASD).

Blood tests to look at platelet count and blood factors may reveal signs of a bleeding tendency.

Specific tests depend on the symptoms present. 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 mutations in the PTPN11 gene.