Editors Note: Ophanet is a European website providing information about orphan drugs and rare diseases‘. It annually publishes the prevalence of rare diseases; this report series begins with the most prevalent.
Noonan syndrome* is a condition that affects many areas of the body. It is characterized by mildly unusual facial characteristics, short stature, heart defects, bleeding problems, skeletal malformations, and many other signs and symptoms.
People with Noonan syndrome have distinctive facial features such as a deep groove in the area between the nose and mouth (philtrum), widely spaced eyes that are usually pale blue or blue-green in color, and low-set ears that are rotated backward. Affected individuals may have a high arch in the roof of the mouth (high-arched palate), poor alignment of the teeth, and a small lower jaw (micrognathia). Many children with Noonan syndrome have a short neck and both children and adults may have excess neck skin (also called webbing) and a low hairline at the back of the neck.
Approximately 50 to 70 percent of individuals with Noonan syndrome have short stature. At birth, they are usually of normal length and weight, but growth slows over time. Abnormal levels of growth hormone may contribute to the slow growth.
Individuals with Noonan syndrome often have either a sunken chest (pectus excavatum) or a protruding chest (pectus carinatum). Some affected people may also have an abnormal side-to-side curvature of the spine (scoliosis).
Most people with Noonan syndrome have a heart defect. The most common heart defect is a narrowing of the valve that controls blood flow from the heart to the lungs (pulmonary valve stenosis). Some affected individuals have hypertrophic cardiomyopathy, which is a thickening of the heart muscle that forces the heart to work harder to pump blood.
Estimated prevalence 50 per 100,000