What Is Noonan Syndrome?

Medically Reviewed by Dan Brennan, MD on February 09, 2023

• What Causes It?
• What Are the Symptoms?
• How’s It Diagnosed?
• What’s the Treatment?

Noonan syndrome is a rare genetic disorder. If you have it, you might have certain identifiable facial features, short height, and unusual chest shape. You may also have heart defects.

It can cause a wide range of other physical and developmental symptoms that usually start at birth.

There’s no cure for it, but doctors can treat some of the symptoms as they happen.

What Causes It?

Noonan syndrome is caused by a genetic defect. Scientists have identified four genes involved in the syndrome: PTPN11, SOS1, RAF1, and KRAS.

There are two ways you can get this syndrome:

• The gene mutation is passed down to you by one parent
• The altered gene happens for the first time while you are still in the womb

What Are the Symptoms?

There are many symptoms, and they may be mild, moderate, or severe.

• Widely spaced eyes
• Deep groove between the nose and mouth
• Low-set ears that arch backward
• Short neck
• Extra skin on the neck (“webbing”)
• Small lower jaw
• High arch in the roof of the mouth
• Crooked teeth

Bones and Chest

• Short height (about 70% of patients)
• Either sunken or protruding chest
• Low-set nipples
• Scoliosis

Most babies with Noonan syndrome are also born with heart disease. They may have:

• Narrowing of the valve that moves blood from the heart to the lungs
• Swelling and weakening of the heart muscle
• Atrial septal defects

• Excessive bruising
• Nosebleeds
• Prolonged bleeding after an injury or surgery
• Blood cancer (leukemia)

• Delayed puberty
• Testes that don’t descend -- this can cause infertility

Other Symptoms

• Vision or hearing problems
• Feeding problems (these usually improve by age 1 or 2)
• Mild intellectual or development disability (although most have normal intelligence)
• Puffy feet and hands (in infants)

How’s It Diagnosed?

Before your baby is born, your doctor might consider that he has Noonan syndrome if a pregnancy ultrasound shows:

• Extra amniotic fluid around your baby in the amniotic sac
• A cluster of cysts in your baby’s neck
• Problems with their heart structure or other structural problems

Your doctor might also suspect Noonan syndrome if you have abnormal results on a specialized prenatal test, called a maternal serum triple screen.

Most of the time, they’ll know your baby has this condition at birth or shortly after by examining them. But sometimes, it’s hard to recognize and diagnose.

What’s the Treatment?

There isn’t one. But your doctor will prescribe treatments for your baby’s symptoms or complications. For example, growth hormones may help with growth problems.

What Else Should I Know?

If you have Noonan syndrome, you may wonder if your future children will have it. That depends on your family’s history

If one of your parents has the condition, they have a 50% chance of passing it on to you.

But if you have Noonan syndrome and no one else in your family had it, the defective gene may have started with you. Doctors call this a “de novo mutation.” In this case, your chances of passing it along to a future child are very small -- less than 1%.

If you’re concerned, see a genetic specialist. They can run tests to spot mutations that happen with this syndrome, and help confirm whether your child has it or not.