Noonan syndrome is a genetic disorder that is present from birth. It involves a variety of distinguishing features and health issues.
It is often associated with congenital heart disease, short stature, and unusual facial features.
According to the National Organization for Rare Disorders, Noonan syndrome is thought to affect approximately 1 in 1,000 to 1 in 2,500 people.
Some reports suggest it may be more common than this, but misdiagnosis or under-diagnosis makes it difficult to determine the true prevalence.
Noonan’s syndrome is a genetic condition.
Noonan syndrome is caused by an abnormality or mutation in one of several genes.
The faulty gene associated with Noonan syndrome can be:
Inherited from a parent. Approximately 50 percent of people with the condition have an affected parent. The parent carrying the genetic abnormality may or may not have any obvious features of the disorder.
A new mutation that randomly occurs in children without any genetic predisposition.
Having a parent with Noonan syndrome is the greatest risk factor for development of the condition. The risk of passing the defective gene from parent to child is 50 percent for each pregnancy.
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Issues with growth and development
Noonan syndrome may involve growth and developmental issues.
People with the condition may:
Have a normal birthweight, but experience delayed growth over time
Show low levels of growth hormones
Go through puberty a few years later than the average
Fail to experience normal growth spurts during puberty
Some people with Noonan syndrome reach normal height by adulthood, but the average height is 5 feet and 3 inches for men with the condition, and 5 feet for women.
Most people with Noonan syndrome have some form of congenital heart disease.
Examples of the types of heart defects they may have are:
Pulmonary stenosis: A narrowing of the pulmonary valve, which helps control blood flow from the heart to the lungs. The heart is under greater pressure to ensure blood is pumped into the lungs. This may occur alone in those with Noonan syndrome, or with other heart defects.
Hypertrophic cardiomyopathy: The muscles of the heart become enlarged, placing strain on the heart.
Septal defects: A hole in the heart which separates the two lower chambers of the heart. Small defects don’t cause symptoms, but larger ones cause the heart and lungs to work harder.
Irregular heartbeat: This occurs in most people with Noonan syndrome, with or without abnormal heart structures.
Other signs and symptoms
A variety of other issues can arise.