Alternative names
Noonan syndrome

Definition
Noonan syndrome is a genetic disorder that causes abnormal development of multiple parts of the body. In particular there is webbing of the neck and different shapes to the chest that are reminiscent of Turner syndrome, hence the former name Turner-like syndrome.

Causes, incidence, and risk factors

Noonan syndrome can be inherited in an autosomal dominant manner. It affects at least 1 in 2,500 children. The fact that some children do not have a parent with Noonan syndrome likely reflects sporadic inheritance, that is, presumably the occurrence of a new mutation. The first specific gene that causes Noonan syndrome, called PTPN11, was discovered in 2001. It is expected that other genes will be discovered that cause Noonan syndrome.

Frequently seen abnormalities include webbing of the neck, changes in the sternum (usually a sunken chest called pectus excavatum), facial abnormalities, and congenital heart disease (especially pulmonic stenosis). Because these abnormalities resemble those of Turner syndrome (which only affects females), Noonan syndrome used to be called “male Turner syndrome,” this term is no longer used because Noonan syndrome can affect females also.

Facial abnormalities may include low-set or abnormally shaped ears, sagging eyelids (ptosis), wide-set eyes (hypertelorism), epicanthal folds, and a small jaw (micrognathia). Mild mental retardation is present in about 25% of cases. Hearing loss varies. Puberty is usually delayed, and males may have undescended testicles and a small penis. Adult height is usually decreased.

Symptoms

 
• webbed and short appearing neck  
• sternum abnormalities (pectus excavatum, occasionally pectus carinatum)  
• sagging eyelids (ptosis)  
• wide-set (hypertelorism) or down-slanting eyes  
• low-set or abnormally shaped ears  
• undescended testicles  
• delayed puberty  
• mental retardation in only a quarter of patients  
• short stature  
• small penis

Signs and tests

Examination may show an extra fold of skin above the eyes (epicanthal folds). The eyes may also appear down-slanted (antimongoloid palpebral slant). The arms may be held at an unusual angle (cubitus valgus). There may be signs of congenital heart disease (often pulmonic stenosis, occasionally ASD). There may be a bleeding tendency revealed by low platelet count or coagulation tests and measuring the levels of specific coagulation factors in the blood (factors XI-XIII).

Testing will depend on the symptoms present. For example, if there are signs of Heart disease, an ECG, chest x-ray or echocardiogram may be recommended. Hearing tests are indicated if there is any sign of decreased hearing.

Genetic testing has two purposes. First, a karyotype analysis can make sure that no easily detected abnormality of chromosomes can be mistaken for Noonan syndrome. Second, research genetic testing for mutations in the PTPN11 gene may be available.

Treatment
There is no single treatment for Noonan syndrome. Treatment focuses on the problems that occur. Growth hormone has been used successfully in Noonan syndrome to treat short stature.

Support Groups
The Noonan Syndrome Support Group, Inc. 888-686-2224; http://www.noonansyndrome.org

Expectations (prognosis)
The expected outcome depends on the extent and severity of symptoms that are present. Patients can lead normal lives. Mental retardation, if present, is usually mild.

Complications

 
• low self-esteem  
• social difficulties related to physical abnormalities  
• male infertility in those with both testes undescended  
• abnormal heart structure  
• accumulation of fluid in tissues of body (lymphedema, cystic hygroma)  
• failure to thrive in infants  
• short stature

Calling your health care provider
This condition may be detected on early infant examinations. Evaluation by an experienced geneticist is often needed to determine a diagnosis of Noonan syndrome. If there are any signs of Noonan or Turner syndrome ask your health care provider for the name of a geneticist to see. Genetic counseling is recommended if you have a family history of Noonan syndrome.

Prevention
People with a family history of Noonan syndrome may want to consult with their health care provider before having children, although at this time there are no tests to detect the tendency for this disorder. Prevention of complications, such as Heart disease, depends on early detection and continuing care of a cardiologist.

Medical Encyclopedia

All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.