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? »
- Turner Syndrome - Learn about Turner syndrome, an abnormality in the X chromosome of females that leaves them infertile. Symptoms also include a webbed neck, puffiness of the hands and feet, heart defects, and kidney problems.
- Birth Defects - Read about birth defects, the leading cause of infant mortality during the first year. Causes of birth defects include ingestion of drugs or alcohol during pregnancy, genetic, hereditary, or environmental factors.
- Genetic Disease - Learn about genetic disease caused by abnormalities in an individual's genome. There are four types of genetic inheritance, single, multifactoral, chromosome abnormalities, and mitochondrial inheritance. Genetic testing is available for some genetic diseases.
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