Noonan syndrome is a genetic disorder that affects approximately 1 in 1000 to 2500 people. Signs and symptoms can vary greatly from person to person, so this condition can be underdiagnosed or even misdiagnosed.
Here’s more information about the causes of Noonan syndrome, the signs and symptoms, and questions you may want to ask your doctor.
Noonan syndrome is a congenital condition, which means it is present at birth.
It can result from one of eight different genetic mutations and can be inherited from a parent who carries an affected gene (called autosomal dominant inheritance). However, it can also be spontaneous, that is, it can occur randomly without any family history.
People with Noonan syndrome may have certain facial features, heart defects, short stature, or other physical and developmental problems.
Since signs and symptoms can vary widely from person to person, some babies may be diagnosed at birth while others may not be diagnosed until later in life.
There is no cure for the syndrome, so treatment is focused on addressing a person’s specific health issues.
Although Noonan syndrome with multiple lentigines (NSML) is similar to Noonan syndrome, it is a different disorder.
Both are caused by PTPN11 and RAF1 genetic mutations and, therefore, they share various characteristics. In fact, it can be difficult to tell the difference between the two until later in childhood.
But NSML is very rare. Additionally, children with this disorder may develop patches of skin called lentigines when they are
Not everyone with NSML will develop lentigines, but it’s a classic feature of the syndrome along with other issues, like heart defects, short stature, hearing problems, and certain facial features.
There are many symptoms of Noonan syndrome. Their severity ranges from mild to severe.
Symptoms may include:
- Some facial features: wide-set eyes, low ears, broad nose and forehead, small jaw
- Eye conditions: ptosis (droopy eyelids), wide distance between the eyes, amblyopia (lazy eye), astigmatism, strabismus
- Hearing problems: hearing loss (specifically, sensorineural deafness)
- Cardiovascular problems: pulmonary stenosis (heart valve problem), irregular heartbeat, atrial or ventricular septal defects, hypertrophic cardiomyopathy (thickening of the heart muscle)
Other issues, such as:
- Musculoskeletal problems: atypical curvature of the spine (kyphosis, scoliosis), abnormalities of the sternum or elbows
- Blood problems: blood clotting problems leading to increased bruising/bleeding, atypical white blood cell count
- Lymphatic conditions: lymphedema (accumulation of fluid in the lymphatic system)
- Reproductive issues: undescended testicles and infertility in men
- Kidney disorders: absence of a kidney, for example
- Skin diseases: loose skin on the neck, thick skin on the palms of the hands, benign tumors on the skin, black/brown spots on the skin (lentigines are similar to liver spots)
Developmental issues, such as:
- Growth issues: apparent short stature around the child’s second birthday (without treatment, the average adult height of women with Noonan syndrome is 5 feet and 5 feet and 3 inches For men)
- Learning disabilities: some people People with Noonan syndrome may experience mild learning disabilities or a lower IQ.
- Other issues: eating and behavior problems are other possibilities, although they are less common
Noonan syndrome can be inherited from a parent or arise spontaneously during conception.
There are eight genetic mutations that may be linked to the syndrome. These mutations in these five genes are most associated with the disease:
However, in 1 out of 5 people with Noonan syndrome, no specific genetic changes can be found. And an individual’s symptoms tend to be linked to the genetic change responsible for the syndrome.
About 30 to 75 percent people with Noonan syndrome inherit it from a parent with a genetic mutation. This means that the parent with the genetic mutation also has Noonan syndrome, but their symptoms may be so mild that they were never diagnosed or may have been misdiagnosed.
For other people with Noonan syndrome, the genetic mutation occurs randomly.
At birth, your child’s doctor may observe certain physical signs, such as facial features or congenital heart problems. From there, the diagnosis can be confirmed with a blood test to look for genetic mutations.
However, a negative blood test does not always mean that a child does not have Noonan syndrome. In 1 out of 5 casesno genetic mutation is found.
As your child grows, other tests may be ordered to look at specific health issues. They understand:
You may also be able to get diagnosed while pregnant. If you think you or your partner have the genetic mutation, your doctor may suggest genetic testing, such as amniocentesis or chorionic villus sampling.
An ultrasound can also identify certain signs, such as excess amniotic fluid (polyhydramnios) or fluid buildup in other parts of the body.
Since there is no cure for the syndrome as a whole, treatment focuses on addressing specific health conditions or symptoms.
Treatment can involve anything from medications to surgery to ongoing medical appointments to monitor different conditions.
Treatment may include:
- surgery to treat congenital heart conditions, such as pulmonary stenosis and septal abnormalities
- medicines for heart problems, such as hypertrophic cardiomyopathy
- regular appointments to monitor heart conditions
- medication (growth hormone) for restricted growth
- speech therapy for eating and speaking problems
- undescended testicle surgery
- glasses or surgery to treat eye problems
- regular appointments and treatment as needed for hearing problems
- treatment as needed for lymphatic problems
- medicine to help blood clot
- early intervention (physiotherapy and occupational therapy) and other therapies to treat learning disabilities and other developmental delays
Overall, you will need to work closely with your child’s doctors to address your child’s health issues. It helps if your doctors can work together so everyone is on the same page with your child’s care.
With the proper medical care and therapies, many children with Noonan syndrome are likely to lead healthy lives as they reach adulthood.
Not only that, but it’s also important to note that new symptoms or medical issues don’t usually develop as children get older.
Every child is affected by Noonan syndrome in a different way, so the outlook is very individual. Congenital heart defects – especially left ventricular disease – are the biggest concern when it comes to adverse health effects.
Parents who carry the genetic mutations associated with Noonan syndrome have a 50 percent chance of transmitting the mutation with each pregnancy.
So, if you have a family history of the condition, you may want to consider making an appointment with a genetic counselor to assess your risk.
If you have no family history of the disease and have a child with Noonan syndrome, your chances of encountering it again are much lower. Less than 1 percent couples in which neither parent has Noonan syndrome have another child with the disease.
As for the causes of Noonan syndrome, scientists are not so sure. There is currently no research to suggest that it is caused by exposure to radiation, diet, or any other environmental factor.
Many children with Noonan syndrome can live full and healthy lives with the right medical treatment and therapies. And you don’t have to navigate these waters alone.
Contact your child’s doctor for advice, support, and help in finding additional resources to help you on your journey.
The Noonan Syndrome Foundation is another excellent source of information, education and advocacy.