Noonan syndrome is a genetic condition that affects around 1 in every 1,000–2,500 people. The signs and symptoms can vary greatly from person to person, so this condition may be underdiagnosed or even misdiagnosed.

Here’s more about what causes Noonan syndrome, what the signs and symptoms are, and what questions you may want to ask your doctor.

Noonan syndrome is a congenital disorder, which means it’s present at birth.

It may result from any of eight different gene mutations and can be inherited from a parent who carries an affected gene (referred to as autosomal dominant inheritance). However, it may also be spontaneous, meaning it can happen at random without any family history.

People with Noonan syndrome may have certain facial features, heart defects, short stature, or other physical and developmental issues.

Since signs and symptoms can vary greatly from person to person, some babies may be diagnosed at birth while others may not be diagnosed until later in life.

There’s no cure for the syndrome, so treatment is focused on addressing whatever specific health issues a person has.

Though Noonan syndrome with multiple lentigines (NSML) is similar to Noonan syndrome, it’s a different disorder.

Both are caused by PTPN11 and RAF1 gene mutations and, as a result, they share various characteristics. In fact, it may be difficult to tell the difference between the two until later on in childhood.

But NSML is very rare. Also, children with this disorder may develop skin spots called lentigines by the time they’re 4 or 5 years old. When children reach puberty, these spots may number in the thousands.

Not all people with NSML will develop lentigines, but it’s a classic feature of the syndrome along with other issues, like heart defects, short stature, hearing issues, and certain facial features.

There are many symptoms of Noonan syndrome. They range in severity from mild to serious.

Symptoms may include:

Other issues, such as:

  • Musculoskeletal issues: atypical curvature of the spine (kyphosis, scoliosis), abnormalities of the breastbone or elbows
  • Blood issues: blood clotting problems leading to increased bruising/bleeding, atypical white blood cell count
  • Lymphatic conditions: lymphedema (buildup of fluid in the lymphatic system)
  • Reproductive issues: undescended testes and infertility in males
  • Kidney conditions: absence of a kidney, for example
  • Skin conditions: loose skin on neck, thick skin on palms of hands, benign tumors on the skin, black/brown spots on the skin (lentigines are similar to liver spots)

Developmental concerns, such as:

  • Growth issues: short stature apparent around child’s second birthday (without treatment, the average adult height for females with Noonan syndrome is 5 feet and 5 feet and 3 inches for males)
  • Learning disabilities: some people with Noonan syndrome may experience mild learning disabilities or lower IQ.
  • Other issues: problems with feeding and behavior are other possibilities, though they’re less common

Noonan syndrome can either be inherited from a parent or happen spontaneously during conception.

There are eight gene mutations that can be linked to the syndrome. These mutations in these five genes are most associated with the disorder:

  • PTPN11
  • SOS1
  • RIT1
  • RAF1
  • KRAS

However, in 1 out of every 5 people with Noonan syndrome, no specific gene change can is ever found. And an individual’s symptoms tend to relate to the gene change responsible for the syndrome.

For example, the PTPN11 gene, which is found in around 50 percent of people with Noonan syndrome, is associated with pulmonic stenosis.

About 30 to 75 percent of people with Noonan syndrome inherit it from a parent who carries a gene mutation. This means that the parent with the gene mutation also actually has Noonan syndrome, too, but their symptoms may be so mild that they’ve never been diagnosed or may have been misdiagnosed.

For other people with Noonan syndrome, the genetic mutation happens randomly.

At birth, your child’s doctor may observe certain physical signs, facial features, for instance, or congenital heart issues. From there, diagnosis can be confirmed via a blood test to look for genetic mutations.

A negative blood test doesn’t always mean that a child doesn’t have Noonan syndrome, though. In 1 out of 5 cases, no genetic mutation is found.

As your child grows, other tests may be ordered to look at specific health issues. They include:

You may also be able to get a diagnosis during pregnancy. If you suspect that you or your partner carry the gene mutation, your doctor may suggest genetic testing, like amniocentesis or chorionic villus sampling.

An ultrasound scan can also identify certain signs, like excess amniotic fluid (polyhydramnios) or fluid buildup in other parts of the body.

Questions for your doctor or healthcare professional

You may have a number of questions if your child has been diagnosed with Noonan syndrome. Be sure to write them down before your next appointment so you won’t forget.

Questions might include:

  • Should I consider being tested for Noonan syndrome or other genetic conditions before or during pregnancy?
  • What are the risks associated with such testing?
  • Do my child’s signs/symptoms suggest my child may have Noonan syndrome?
  • What further testing is needed for diagnosis?
  • What health complications or developmental concerns may my child’s face?
  • What treatments and therapies are available?
  • What doctors or specialists should I see during pregnancy/after my child is born?
  • Where can I find more information or support?
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Since there’s no cure for the syndrome as a whole, treatment is focused on addressing specific health conditions or symptoms.

Treatment can involve anything from medication to surgery to ongoing doctor appointments to monitor different conditions.

Treatment may include:

  • surgery to address congenital heart disease, like pulmonary stenosis and septal defects
  • medication for heart issues, like hypertrophic cardiomyopathy
  • regular appointments to monitor heart conditions
  • medication (growth hormone) for restricted growth
  • speech therapy for feeding and speech issues
  • surgery for undescended testicles
  • glasses or surgery to address eye issues
  • regular appointments and treatment as needed for hearing issues
  • treatment as needed for lymphatic issues
  • medication to help with blood clotting
  • early intervention (physical and occupational therapy) and other therapies to address learning disabilities and other developmental delays

Overall, you’ll need to work closely with your child’s doctors to treat any health issues your child has. It’s helpful if your doctors can work together so everyone is on the same page with your child’s care.

The medical team that may treat a child with Noonan syndrome

Treatment for Noonan syndrome is usually done with a team approach with doctors and specialists from different medical disciplines. Your child’s medical team may include the following professionals:

  • Maternal-fetal medicine specialists: doctors who specialize in high-risk pregnancies
  • Neonatologists: doctors who treat babies in the NICU after birth
  • Pediatricians: primary care doctors who treat children specifically
  • Pediatric cardiologists: doctors who treat heart conditions in children
  • Pediatric hematologists: doctors who treat blood conditions in children
  • Pediatric endocrinologists: doctors who treat hormone and growth conditions in children
  • Pediatric ophthalmologists: doctors who treat eye conditions in children
  • Genetic counselors: professionals who diagnose and provide information about inherited disorders
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With the right medical care and therapies, many children with Noonan syndrome are likely to live healthy lives as they grow into adulthood.

Not only that, but it’s also important to note that new symptoms or medical issues don’t typically develop as kids get older.

Each child is affected by Noonan syndrome in a different way, so the outlook is highly individual. Congenital heart defects — in particular, left ventricular disease — are the biggest concern with regard to adverse health outcomes.

Parents who carry the gene mutations associated with Noonan syndrome have a 50 percent chance of passing along the mutation with each pregnancy.

So, if you have a family history of the disorder, you may consider making an appointment with a genetic counselor to evaluate your risk.

If you don’t have a family history of the disorder and you have one child with Noonan syndrome, your chances of encountering it again are much lower. Fewer than 1 percent of couples in which neither parent has Noonan syndrome go on to have another child with the condition.

As far as what causes Noonan syndrome to begin with, scientists aren’t so sure. There’s currently no research to suggest that it’s caused by exposure to radiation, diet, or any other environmental factors.

Many children with Noonan syndrome can live full, healthy lives with the right medical treatment and therapies. And you don’t have to navigate these waters all on your own.

Reach out to your child’s doctor for guidance, support, and for help finding additional resources to aid you in your journey.

The Noonan Syndrome Foundation is another great source for information, education, and advocacy.