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Noonan syndrome

Definition

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.

Causes

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.

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

Exams and Tests

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.

Treatment

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.

Support Groups

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

Outlook (Prognosis)

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

Possible Complications

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

When to Contact a Medical Professional

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.

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