Noonan Syndrome

Noonan syndrome is a developmental disorder characterized by unusual facial characteristics, short stature, heart defects, bleeding problems, and skeletal malformations. Eye abnormalities occur in up to 95 percent of people with Noonan syndrome. Problems with language and speech are common. Puberty for both males and females with Noonan syndrome is usually delayed for approximately two years. Most males with this disorder have undescended testicles (cryptorchidism) which can lead to infertility (inability to father a child) later in life. The majority of children diagnosed with Noonan syndrome have normal intelligence, but a small percentage have special educational needs, and some have mental retardation.

How common is Noonan syndrome?

Noonan syndrome occurs in approximately 1 in 1,000 to 2,500 people.

What genes are related to Noonan syndrome?

Mutations in the KRAS, PTPN11, RAF1, and SOS1 genes cause Noonan syndrome.

Approximately 50 percent of individuals with Noonan syndrome have mutations in the PTPN11 gene. Mutations in the SOS1 gene are seen in 20 percent of those with Noonan syndrome. Mutations in the RAF1 gene account for between 10 and 15 percent of Noonan syndrome cases. About 5 percent of people with Noonan syndrome have mutations in the KRAS gene and usually have a more severe or atypical form of the disorder. The cause of Noonan syndrome in the remaining 10 to 15 percent of people with this disorder is unknown.

The PTPN11, SOS1, KRAS, and RAF1 genes all provide instructions for making proteins that are important for the proper formation of several types of tissue during development. These proteins also play roles in cell division, cell movement, and cell differentiation (the process by which cells mature to carry out specific functions).

Mutations in the PTPN11 gene, SOS1 gene, KRAS gene, or RAF1 gene cause the resulting protein to be continuously active, rather than switching on and off in response to signals that control growth and development. This constant activation disrupts the regulation of systems that control cell growth and division, leading to the characteristic features of Noonan syndrome.

Read more about the KRAS, PTPN11, RAF1, and SOS1 genes.

How do people inherit Noonan syndrome?

This condition is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder.

In some cases, an affected person inherits the mutation from one affected parent. Other cases may result from new mutations in the gene. These cases occur in people with no history of the disorder in their family.

Where can I find information about treatment for Noonan syndrome?

These resources address the management of Noonan syndrome and may include treatment providers.

• Gene Review: Noonan Syndrome
• Genetic Alliance
• MedlinePlus Encyclopedia: Noonan Syndrome

You might also find information on treatment of Noonan syndrome in Educational resources and Patient support.

Where can I find additional information about Noonan syndrome?

You may find the following resources about Noonan syndrome helpful. These materials are written for the general public.

• MedlinePlus - Health information (5 links)
• Educational resources - Information pages (4 links)
• Patient support - For patients and families (6 links)

You may also be interested in these resources, which are designed for healthcare professionals and researchers.

• Gene Reviews - Clinical summary
• Gene Tests - DNA tests ordered by healthcare professionals (4 links)
• ClinicalTrials.gov - Linking patients to medical research
• PubMed - Recent literature
• OMIM - Genetic disorder catalog (5 links)

What other names do people use for Noonan syndrome?

• familial Turner syndrome
• Female Pseudo-Turner Syndrome
• Male Turner Syndrome
• Noonan-Ehmke syndrome
• pseudo-Ullrich-Turner syndrome
• Turner-like syndrome
• Turner's phenotype, karyotype normal
• Turner syndrome in female with X chromosome
• Ullrich-Noonan syndrome

What if I still have specific questions about Noonan syndrome?

• See How can I find a genetics professional in my area? in the Handbook.
• Ask the Genetic and Rare Diseases Information Center.
• Submit your question to Ask the Geneticist.

Where can I find general information about genetic conditions?

The Handbook provides basic information about genetics in clear language.

• What does it mean if a disorder seems to run in my family?
• What are the different ways in which a genetic condition can be inherited?
• If a genetic disorder runs in my family, what are the chances that my children will have the condition?
• Why are some genetic conditions more common in particular ethnic groups?

These links provide additional genetics resources that may be useful.

• Genetics and health
• Resources for Patients and Families
• Resources for Health Professionals

What glossary definitions help with understanding Noonan syndrome?

atypical ; autosomal ; autosomal dominant ; cell ; cell division ; chromosome ; cryptorchidism ; differentiation ; familial ; gene ; infertility ; karyotype ; malformation ; mental retardation ; mutation ; new mutation ; phenotype ; protein ; puberty ; stature ; syndrome ; testicles ; tissue ; undescended testicle

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.