Health Encyclopedia

Noonan syndrome

Definition

Noonan syndrome is a disease present from birth (congenital) that causes many parts of the body to develop abnormally. In some cases it is passed down through families (inherited).

Causes

Noonan syndrome is linked to defects in several genes. In general, certain proteins involved in growth and development become overactive as a result of these gene changes.

Noonan syndrome is an autosomal dominant condition. This means only one parent has to pass down the nonworking gene for the child to have the syndrome. However, some cases may not be inherited.

Symptoms

Symptoms include:

Delayed puberty
Down-slanting or wide-set eyes
Hearing loss (varies)
Low-set or abnormally shaped ears
Mild intellectual disability (only in about 25% of cases)
Sagging eyelids (ptosis)
Short stature
Small penis
Undescended testicles
Unusual chest shape (most often a sunken chest called pectus excavatum)
Webbed and short-appearing neck

Exams and Tests

The health care provider will perform a physical exam. This may show signs of heart problems the infant had from birth. These may include pulmonary stenosis and atrial septal defect.

Tests depend on the symptoms, but may include:

Platelet count
Blood clotting factor test
ECG, chest x-ray, or echocardiogram
Hearing tests
Growth hormone levels
Renal ultrasound

Genetic testing can help diagnose this syndrome.

Treatment

There is no specific treatment. Your provider will suggest treatment to relieve or manage symptoms. Growth hormone has been used successfully to treat short height in some people with Noonan syndrome.

Support Groups

More information and support for people with Noonan syndrome and their families can be found at -- www.teamnoonan.org.

Possible Complications

Complications may include:

Abnormal bleeding or bruising
Buildup of fluid in tissues of body (lymphedema, cystic hygroma)
Failure to thrive in infants
Leukemia and other cancers
Low self-esteem
Infertility in males if both testes are undescended
Problems with the structure of the heart
Short height
Social problems due to physical symptoms

When to Contact a Medical Professional

This condition may be found during early infant exams. A 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.

References

Cooke DW, Divall SA, Radovick S. Normal and aberrant growth in children. In: Melmed S, Auchus RJ, Goldfine AB, Koenig RJ, Rosen CJ, eds. Williams Textbook of Endocrinology. 14th ed. Philadelphia, PA: Elsevier; 2020:chap 25.

Madan-Khetarpal S, Arnold G, Ortiz D. Genetic disorders and dysmorphic conditions. In: Zitelli BJ, McIntire SC, Nowalk AJ, Garrison J, eds. Zitelli and Davis' Atlas of Pediatric Physical Diagnosis. 8th ed. Philadelphia, PA: Elsevier; 2023:chap 1.

Mitchell AL. Congenital anomalies. In: Martin RJ, Fanaroff AA, Walsh MC, eds. Fanaroff and Martin's Neonatal-Perinatal Medicine. 11th ed. Philadelphia, PA: Elsevier; 2020:chap 30.

Review Date:1/6/2022
Reviewed By:Anna C. Edens Hurst, MD, MS, Associate Professor in Medical Genetics, The University of Alabama at Birmingham, Birmingham, AL. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

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