About Noonan Syndrome

Noonan syndrome is a disorder that involves unusual facial characteristics, short stature, heart defects present at birth, bleeding problems, developmental delays, and malformations of the bones of the rib cage.

Noonan syndrome is caused by changes in one of several autosomal dominant genes. A person who has Noonan syndrome may have inherited an altered (mutated) gene from one of his or her parents, or the gene change may be a new change due to an error carried by the egg or sperm or occurring at conception. Alterations in four genes - PTPN11, SOS1, RAF1 and KRAS - have been identified to date.

Noonan syndrome is present in about 1 in 1,000 to 1 in 2,500 people.

Symptoms of Noonan syndrome may include the following:

• A characteristic facial appearance.

• Short stature.

• Heart defect present at birth (congenital heart defect).

• A broad or webbed neck.

• Minor eye problems such as strabismus in up to 95 percent of individuals.

• Bleeding problems such as a history of abnormal bleeding or bruising.

• An unusual chest shape with widely-spaced and low set nipples.

• Developmental delay of varying degrees, but usually mild.

• In males, undescended testes (cryptorchidism).

The diagnosis of Noonan syndrome is based on the person's clinical symptoms and signs. The specialist examines the person looking for the specific features of Noonan syndrome.

Individuals who have Noonan syndrome have normal chromosome studies. Four genes - PTPN11, SOS1, RADF1and KRAS - are the only genes that are known to be associated with Noonan syndrome. Approximately 50 percent of individuals with Noonan syndrome have mutations in the PTPN11 gene. Twenty percent of those with Noonan Syndrome have mutations in the SOS1. 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 not yet known. .

Symptoms of Noonan syndrome may include the following:

• A characteristic facial appearance.

• Short stature.

• Heart defect present at birth (congenital heart defect).

• A broad or webbed neck.

• Minor eye problems such as strabismus in up to 95 percent of individuals.

• Bleeding problems such as a history of abnormal bleeding or bruising.

• An unusual chest shape with widely-spaced and low set nipples.

• Developmental delay of varying degrees, but usually mild.

• In males, undescended testes (cryptorchidism).

Treatment for individuals who have Noonan syndrome is based on their particular symptoms. Heart problems are treated in the same way as they are for individuals in the general population. Early intervention programs are used to help with developmental disabilities, when present. Bleeding problems that can be present in Noonan syndrome may have a variety of causes and are treated according to their cause. Growth problems may be caused by lack of growth hormone and may be treated with growth hormone treatment. Symptoms such as heart problems are followed on a regular basis.

Noonan syndrome is inherited in families in an autosomal dominant pattern. This means that a person who has Noonan syndrome has one copy of an altered gene that causes the disorder. In about one-third to two-thirds of families one of the parents also has Noonan syndrome. The parent who has Noonan syndrome has a 1 in 2 (50 percent) chance to pass on the altered gene to a child who will be affected; and a 1 in 2 (50 percent) chance to pass on the normal version of the gene to a child who will not have Noonan syndrome. In many individuals who have Noonan syndrome, the altered gene happens for the first time in them, and neither of the parents has Noonan syndrome. This is called a de novo mutation. The chance for these parents to have another child with Noonan syndrome is very small (less than 1 percent).

Additional Resources on Noonan Syndrome

• Genetics Home Reference: Noonan syndrome

• Noonan Syndrome Foundation

• Medline Plus: Noonan syndrome

• Medscape: Noonan Syndrome

• Mayo Clinic: Noonan Syndrome

• GARD: Noonan Syndrome