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Noonan Syndrome Information

  • Published: 2013-01-20 (Revised/Updated 2014-04-20) : Author: Disabled World
  • Synopsis: Condition affects many areas of the body including unusual facial characteristics, heart defects, short stature, skeletal malformations, bleeding issues, and other symptoms.

Quote: "Approximately 1 in every 1,000 to 2,500 people experience Noonan syndrome."

Main Document

Noonan syndrome is a condition that affects many areas of a person's body. Mildly unusual facial characteristics, heart defects, short stature, skeletal malformations, bleeding issues, and other signs and symptoms characterize the condition. People who experience Noonan syndrome have distinctive facial features to include a deep groove in the area between their nose and mouth, eyes that are widely spaced and often times blue-green or pale blue in color, as well as ears that are low-set and rotated backward. People with this condition might have a high arch in the roof of their mouth, a small lower jaw, and poor alignment of their teeth. A number of children with Noonan syndrome have a short neck and both children and adults might have excess neck skin referred to as, "webbing," as well as a low hairline at the back of their neck.

A disease that can be passed down through families (inherited). It causes abnormal development in many parts of the body. Noonan syndrome is an autosomal dominant condition. This means only one parent has to pass down the faulty gene for the baby to have the syndrome. However, some cases may not be inherited.

Around 50-70% of people with Noonan syndrome have short stature. At the time of birth they are commonly of average weight and length, but their growth slows over time. Abnormal levels of growth hormone might contribute to their slow growth. People with this condition many times have either a sunken chest or, 'pectus excavatum,' or a protruding chest, 'pectus carinatum.' Some people with Noonan syndrome might also experience a side-to-side curvature of their spine or scoliosis.

The majority of people with Noonan syndrome experience a heart defect. The most common form of heart defect is a narrowing of the valve that controls blood flow from the person's heart to their lungs or, 'pulmonary valve stenosis.' Some people with Noonan syndrome have, 'hypertrophic cardiomyopathy,' which is a thickening of their heart muscle that forces their heart to work harder than it should have to in order to pump blood. A number of bleeding disorders have also been associated with Noonan syndrome. Some people might experience excessive bruising, prolonged bleeding after surgery or an injury, or nosebleeds. Women with a bleeding disorder commonly have excessive bleeding while menstruating, or during childbirth.

Adolescent males with Noonan syndrome commonly experience delayed puberty, going through puberty starting at age 13 or 14 and experiencing a reduced pubertal growth spurt. The majority of males with Noonan syndrome have, 'cryptorchidism,' or undescended testicles that might be related to a delay in puberty or infertility later in their lives. Females with Noonan syndrome commonly have average puberty and fertility, on the other hand.

Noonan syndrome may cause a number of additional signs and symptoms. The majority of children who are diagnosed with Noonan syndrome have average intelligence, although a small percentage have special educational needs, and some experience intellectual disability. Some people with the condition experience hearing or vision issues. Infants with Noonan syndrome might be born with feet or hands that are puffy caused by a buildup of fluid or, 'lymphedema,' that may go away on its own. Infants with this syndrome might also experience issues with feeding, something that commonly improves by age 1 or 2. Older people may develop lymphedema, often in their lower legs or ankles. Other names for Noonan syndrome include the following:

The Genetics of Noonan syndrome

Approximately 1 in every 1,000 to 2,500 people experience Noonan syndrome. Mutations in the SOS1, PTPN11, NRAS, KRAS, and BRAF genes cause Noonan syndrome. Most instances of Noonan syndrome are the result of PTPN11 gene mutations; around half of people with this syndrome have these specific gene mutations.

Mutations to the SOS1 gene account for between 10 to 15 percent, while mutations to the RAF1 gene account for between 5 and 10 percent of people who experience Noonan syndrome. Approximately 2 percent of people with this syndrome have mutations in the KRAS gene and commonly experience a more severe or, 'atypical,' form of the syndrome. Medical science does not know how many people with Noonan syndrome have mutations in the NRAS or BRAF genes, although it is most likely a very small number of people. The cause of Noonan syndrome in the remaining 20 percent of people with the syndrome is not known.

The SOS1, PTPN11, KRAS, RAF1, BRAF, and NRAS genes provide instructions for making proteins that are important in signaling pathways a person needs for the proper formation of a number of types of tissue during development. The proteins also play roles in cell division, movement, and cell differentiation - the process by which cells mature and perform specific functions. Mutations in any one of the genes mentioned cause the resulting protein to be continuously active instead of switching on and off in response to signals from the cell. The constant activation disrupts the regulation systems that control cell division and growth, leading to the features that are characteristic of Noonan syndrome.

How People Inherit Noonan syndrome

Noonan syndrome is inherited in an, 'autosomal dominant pattern.' What this means is one copy of the altered gene in each cell is enough to cause the syndrome. In some instances, a person may inherit the mutation from one parent. At other times, a person may experience the syndrome due to new mutations in the gene. This occurs in people who have no history of the syndrome in their family.

Family Genetic Disorders

A particular genetic disorder might be described as, 'running in a family,' if more than one person in a family has the condition. Some disorders that affect multiple family members are caused by mutations in genes, something that may be inherited or passed down from a parent to a child. Other conditions that appear to run in families are not cause by mutations in single genes. Environmental factors such as a combination of genetic and environmental factors, or dietary habits, are responsible for these disorders.

Determining whether or not a particular condition in a family is inherited is not always easy. A genetics professional may use a person's family history, which is a record of health information about a person's immediate and extended family, to help them determine whether or not a disorder has a genetic component. A genetics professional will ask about the health of people from several generations of the family, commonly first, second, as well as third degree relatives.


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