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November 21, 2009
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Noonan Syndrome

What is Noonan syndrome, and what are the signs and symptoms of this condition?

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.



Next: How do people inherit Noonan syndrome? »

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Noonan Syndrome

What are genetic professionals and what do they do?

Genetics professionals are health care professionals with specialized degrees and experience in medical genetics and counseling. Genetics professionals include geneticists, genetic counselors and genetics nurses.

What is genetic counseling and evaluation?

Genetic professionals work as members of health care teams providing information and support to individuals or families who have genetic disorders or may be at risk for inherited conditions. Genetic professionals:

  • Assess the risk of a genetic disorder by researching a family's history and evaluating medical records.
  • Weigh the medical, social and ethical decisions surrounding genetic testing.
  • Provide support and information to help a person make a decision about testing.
  • Interpret the results of genetic tests and medical data.
  • Provide counseling or refer individual...

Read the Genetic Counseling article »









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