Noonan Syndrome

Noonan syndrome is a genetic condition that can affect many different areas of the body and development. Children who have Noonan syndrome often have recognizable facial features and physical characteristics such as short stature. Delays in reaching developmental milestones like first words or walking are common. It can also affect many other parts of the body, including the heart, eyes, kidneys, digestion, hearing, and growth.

Noonan syndrome is sometimes described as a RASopathy — a term used to describe a group of conditions that are caused by changes in genes that are within the same cellular pathway (the Ras/MAPK pathway). These conditions include Noonan syndrome, Noonan syndrome with multiple lentigines, Cardiofaciocutaneous syndrome (CFC), and Costello syndrome. The conditions have overlapping but distinct features.

Noonan syndrome is a highly variable condition. While there are many potential complications, no individual child has all of them, and those that are present can range in severity from mild to severe. Some features may not be noticed unless an individual is evaluated by a doctor familiar with Noonan syndrome. Possible features include:

• Distinct facial features such as widely spaced eyes with droopy upper eyelids, ears that are set low on the head and rotated slightly back, and a short and wide-appearing neck
• Feeding difficulties
• Chest bone that appears sunken in (pectus excavatum) or pushed out (pectus carinatum)
• Short stature
• Lymphedema (swelling of an extremity), commonly seen as puffy hands or feet in infancy but can also involve the lungs and intestines
• Congenital heart disease, most commonly pulmonary valve stenosis and atrial septal defect (ASD)
• Hypertrophic cardiomyopathy, which is seen in about 20% of children who have Noonan syndrome
• Strabismus, when one or both eyes are not properly aligned and may appear to be looking outward or inward
• Scoliosis, curvature of the spine
• Delays in development, such as speaking later than other children
• Learning concerns which may require extra support in school
• Kidney and genitourinary issues such as undescended testicles (cryptorchidism) and kidney malformation
• Hearing loss
• Bleeding or bruising

Noonan syndrome is caused by a genetic change (also known as a mutation or variant) in an individual’s DNA, or genetic material. The changes responsible for Noonan syndrome occur in regions of DNA called genes. While there are thousands of genes in DNA, changes in only a handful of genes are associated with Noonan syndrome.

A child may be the first person in a family to have Noonan syndrome, caused by a random change in their DNA. In other children, they may have inherited the genetic change from a parent. In most cases of Noonan syndrome, an individual has a 50 percent chance to pass on the genetic change for each child they have. A comprehensive family history evaluation with a geneticist or genetic counselor, along with genetic testing, can help determine the inheritance pattern of Noonan syndrome in your child or family.

Noonan syndrome may be suspected based on the presence of several features or symptoms in your child. A diagnosis can be made by a clinical geneticist who is familiar with the condition.

Genetic testing can also diagnose Noonan syndrome. It is performed through a simple blood or cheek swab test. If your provider recommends genetic testing, a genetic counselor can explain the process of testing, determine the most appropriate test, and review the advantages and limitations of testing. A small percentage of children with a clinical diagnosis of Noonan syndrome will have normal genetic testing, meaning the genetic cause for their diagnosis cannot be identified.

At Boston Children’s Center for Cardiovascular Genetics, you can meet with providers who have expertise in diagnosing and working with children who have Noonan syndrome. Our team provides comprehensive education about the condition and the genetic testing process.

There is no cure for Noonan syndrome, but individual symptoms can be addressed by different providers, including cardiologists, ophthalmologists, endocrinologists, and developmental specialists. A child with a new diagnosis may have several evaluations with many different specialists to make sure they receive appropriate and prompt care, if needed.

A care plan for a child who has Noonan syndrome depends on their specific needs. Many will need evaluations with a variety of different specialists. Our team at the Center for Cardiovascular Genetics has extensive expertise caring for children who have Noonan syndrome. We facilitate referrals to appropriate Boston Children’s programs and specialists based on your child’s specific needs.