Noonan syndrome is a genetic disorder that prevents normal development in various parts of the body. A child may be affected by Noonan syndrome in various ways: unusual facial characteristics, short stature, heart defects, other physical abnormalities and problems, and mental retardation.

The cause of Noonan syndrome is a mutation in one of two genes responsible for making a specific type of protein that plays an important role in the development of the heart, blood cells, bones and other tissues. Noonan syndrome is acquired when a child inherits a copy of an affected gene from a parent. It can also occur as a spontaneous mutation in a child, meaning there's no family history of the disease.

There's no cure for Noonan syndrome, and treatment focuses on managing the disease's symptoms and complications. Growth hormone has been used successfully to treat short stature in some people who have Noonan syndrome.

Facial features
The way your child's face appears is one of the key clinical features leading to a diagnosis of Noonan syndrome. These features will change depending on the age of your child.

• Early infancy. A baby less than 1 month old may have wide-set and down-slanting eyes, low-set ears, a deep groove and wide peaks in the upper lip, a short neck and a low hairline on the back of the head.
• Infancy. An infant may have prominent eyes with a downward slant and thickened lids, and a depressed root of the nose with a wide base and bulbous tip.
• Childhood. There is often a lack of facial expression.
• Adolescence. An adolescent's face is typically wide at the forehead tapering to a pointed chin, the facial features become sharper and the eyes are less prominent, the neck lengthens to reveal skin webbing or prominent neck (trapezius) muscles.
• Adulthood. When a child with Noonan syndrome reaches adulthood, the crease that runs from the edge of the nose to the corner of the mouth becomes prominent and skin appears transparent and wrinkled.

Heart disease
Between 50 percent and 80 percent of children with Noonan syndrome have congenital heart disease, making it one of the key signs and symptoms. Pediatric cardiologists are often the first doctors to see children with Noonan syndrome. Some forms of congenital heart disease are more common when associated with this disorder:

• Pulmonary valve stenosis. This is the most common heart problem seen in children with Noonan syndrome. Pulmonary valve stenosis is a narrowing of the pulmonary valve, the flap of tissue that separates the lower right chamber (ventricle) of your heart from the artery that supplies blood to the lungs (pulmonary artery). The defect may occur by itself, or there can be additional associated defects.
• Hypertrophic cardiomyopathy. This is abnormal growth or thickening of the heart muscle. It may be present at birth or can develop in infancy or childhood.
• Structural defects. Children with Noonan syndrome often have structural defects of the heart. Frequently, the defects involve a hole in the wall that separates the two lower chambers of the heart (ventricular septal defect), or a condition that causes a narrowing of the arteries that carry blood to the lungs for oxygen (pulmonary artery stenosis).

Growth issues
Your child's birth weight will likely be normal, but some children have difficulty with feeding, which can cause poor weight gain until about 18 months. The growth spurt that's usually seen during adolescence may be delayed in your child, but because this disease causes bone maturity to be delayed, your child has the potential to continue growing into his or her 20s. By adulthood, about one-third of people with Noonan syndrome have normal height, but short stature is more commonly seen.

Musculoskeletal issues
An unusually shaped chest often with a sunken sternum (pectus excavatum) or raised sternum (pectus carinatum) is present in 90 percent to 95 percent of children with Noonan syndrome. Wide-set nipples, curvature of the spine (scoliosis or kyphosis) and a short neck, often with extra folds of skin (webbed neck), also are common.

Learning disabilities
Many children with Noonan syndrome get along without difficulty in school — significant mental retardation is uncommon. About a quarter of children with Noonan syndrome have learning disabilities, and some will have a need for special education. It's not uncommon for people with Noonan syndrome to go on to college, and some have earned advanced degrees.

Eye problems
Nearly all people with Noonan syndrome have abnormalities of their eyes and eyelids. Differences in the shape and size of the eyes are hallmark features. Often the iris is pale blue or green. Problems with the eye muscles (strabismus, or crossed eyes), refractive problems (astigmatism, myopia, hypermetropia), rapid movement of the eyeballs (nystagmus) and problems with the nerves of the eyes are common.

Bleeding
Most people with Noonan syndrome have a history of abnormal bruising or bleeding. Sometimes the bleeding problem isn't discovered until a person has surgery and experiences excessive bleeding (hemorrhage).

Neurological problems
Neurological signs and symptoms are less common, but the ones that appear most often are low muscle tone (hypotonia) and joints that hyperextend. Rarely, people with Noonan syndrome experience seizures.

Lymphatic problems
Noonan syndrome can cause problems with the lymphatic system, which drains excess fluid from the body and helps fight infection. These problems can show up before or after birth and can be focused in a particular area of the body or may be widespread. The most common problem is excess fluid (lymphedema) on the back of the hands or top of the feet. It often resolves itself in childhood.

Genitourinary problems
Many people, especially males, with Noonan syndrome can have problems with the kidneys and genitals. Kidney problems are generally mild and occur in a fairly small number of people with the syndrome. Puberty may be delayed in both boys and girls, but most females usually develop normal fertility. In males, however, fertility may not develop normally — often because of undescended testicles, a condition that is common in males with Noonan syndrome. Deficient sex hormones and a small penis also are common in males.

Dermatologic problems
Various dermatologic problems that affect the color and texture of the skin are common. There's also a tendency to develop thick scars after surgery. People with Noonan syndrome often have curly, coarse hair, or sparse hair.

Ears and hearing loss
Chronic inflammation of the middle ear is often a problem in children with Noonan syndrome. As a result, hearing loss is found in about one-third of affected individuals.

It's estimated that Noonan syndrome occurs in one of 1,000 to 2,500 births. The cause is a mutation in one of two genes. The mutation can be inherited from a parent who carries the defective gene (autosomal dominant), or it can develop because of a new mutation in children who don't have a genetic predisposition for the disease.

The two known genes that may mutate and cause Noonan syndrome are:

• PTPN11 gene. About half of people with Noonan syndrome acquire the disorder because of a mutation of a gene called protein tyrosine phosphatase, nonreceptor type 11 (PTPN11). This gene tells your body how to make a protein called SHP-2 (tyrosine phosphatase, nonreceptor type 11). SHP-2 helps your cells know what their job is and when to divide. It's important in the development of your heart, blood cells, bones and other tissues before you are born. But in many people with Noonan syndrome, the PTPN11 gene doesn't work right. It's thought that the genetic mutation causes the SHP-2 protein to be "on" all the time instead of switching on and off in response to signals from other proteins. As a result, systems in your body that control cell function such as growth and division aren't regulated properly. The result is the physical defects that occur in Noonan syndrome.
• KRAS gene. About 5 percent to 10 percent of people acquire the disorder because of a mutation in the gene v-Ki-ras2 Kirsten rat sarcoma viral oncogene homolog (KRAS). This gene is also responsible for making a protein in your body. This protein, called K-Ras, is primarily responsible for regulating cell division. The protein sends signals to a cell's brain (nucleus) that tell it how to grow and divide or when to begin doing a specialized task. When there's a mutation in the KRAS gene, the K-Ras protein is constantly active instead of turning on and off. As a result, cells are instructed to grow and divide all the time, disrupting the normal growth and maturation of various tissues. This happens before you're born and results in the signs and symptoms associated with Noonan syndrome.

In some people, neither of these two genes have a mutation, which may mean that some other, still undiscovered genes cause Noonan syndrome. In rare cases, people who have Noonan syndrome also have another condition called neurofibromatosis 1, which means they have a mutation in the neurofibromin 1 gene. This gene is responsible for making a protein that is also called neurofibromin. This protein acts as a tumor suppressor and helps keep cells from growing too fast or in an uncontrolled way.

Many times the genetics of a child's parents determine whether a child acquires Noonan syndrome. Children who have one parent with Noonan syndrome have a 50 percent chance of getting the disorder themselves.

However, many times the genetic mutations that cause this disease happen spontaneously.

The disease appears equally in males and females.

The signs and symptoms of Noonan syndrome can be subtle. If you suspect your child may have the disorder, or if there's a family history of it, see a doctor with experience diagnosing this condition. Noonan syndrome can be detected with molecular genetic testing. If your unborn child is at risk because of a family history of Noonan syndrome, prenatal tests may be available.

A diagnosis of Noonan syndrome is usually made after a doctor observes some of the key signs and symptoms of the disease, but this can be difficult because some of the features associated with this disorder are subtle and can be hard to identify. Many times, Noonan syndrome isn't diagnosed until adulthood, after a person has a child who is more obviously affected by the condition. Molecular genetic testing can be used to make a definitive diagnosis.

If there's evidence of heart problems, your doctor will likely recommend an electrocardiogram (ECG) and an echocardiogram to assess the type and severity of the condition. The ECG involves placing electrodes on your chest. An ECG looks at the electrical impulses that travel through your heart to assess problems. An echocardiogram uses sound waves to create a moving image of your heart working so that your doctor can see where there may be problems. These tests are usually done by a doctor who specializes in heart conditions (cardiologist).

Many of the symptoms associated with Noonan syndrome are treated just as they would be for anyone else experiencing a health problem. Taken together though, the many problems this disorder can cause will require coordinated management of various symptoms by your doctor and medical specialists who may be part of your health care team.

Sometimes complications can arise that will require special attention depending on the type and severity of the symptoms. These include:

• Developmental issues. If your child is affected developmentally, he or she may have difficulty with organization and spatial sense. Children have also been known to be clumsy, fidgety, stubborn and irritable. Sometimes the developmental challenges are severe enough to require a special plan of action to address your child's learning and educational needs.
• Ear and hearing problems. Chronic or acute inflammation of the middle ear may result in hearing loss.
• Bleeding and bruising. Noonan syndrome can cause excessive bleeding and bruising. This can create problems during surgery or dental work. If excess bleeding and bruising affect you, avoid aspirin or aspirin-containing products because aspirin can thin your blood. Children in general should avoid aspirin because of its association with Reye's syndrome.
• Complications from lymphatic problems. Sometimes fluid can collect in the cavity around the heart and lungs, requiring a chest tube to drain. If the draining is prolonged or needs to be repeated, this can sometimes result in weight loss or infection, and this in turn can lead to additional complications.
• Genitourinary complications. Because of kidney abnormalities, there may be a higher incidence of urinary tract infections. Males may have a low sperm count and other fertility problems because of undescended testicles (cryptorchidism).

Treatment of the symptoms and complications that occur with Noonan syndrome depends on their type and severity. Many of the health and physical issues associated with this disease are treated just the way they are in the general population.

The treatment approach that your doctor may recommend to address various facets of Noonan syndrome may include:

• Heart treatment. Certain drugs may be effective in addressing some kinds of heart problems. If there's a problem with your heart's valves, surgery may be necessary. Your dentist may recommend preventive use of antibiotics prior to dental cleaning or surgeries. Your doctor may also recommend that your heart function be evaluated periodically.
• Treating low growth rate. Many children with Noonan syndrome don't grow at a normal rate. Your child should be measured every six to 12 months to make sure he or she is growing. Noonan syndrome often causes eating difficulties, and your child may not be getting adequate nutrition. Your doctor will likely be checking your child's blood chemistry, thyroid function, bone growth and hormone levels. If your child's growth hormone levels are insufficient, growth hormone therapy may be a successful treatment option. However, this therapy may have a negative effect on other conditions your child may have, such as heart disease.
• Addressing learning disabilities. A wide range of mental and behavioral issues can occur with this condition. Fortunately, there are many successful ways of coping with what are usually mild symptoms. If you discover early that your child has developmental delays, ask your doctor about infant stimulation programs. Physical and speech therapies have been effective in addressing the variety of possible symptoms. In some cases special education or individualized teaching strategies may be appropriate.
• Treatment for neurological problems. If your child has signs or symptoms of neurological problems, your doctor may suggest a complete neurological examination that may include a variety of imaging tests to look at your child's brain. Your doctor may prescribe anticonvulsant drugs if your child has seizures.
• Vision treatments. Because many people with Noonan syndrome have vision problems, your child will need regular eye exams. Most eye issues can be treated with glasses only. Surgery may be needed for some conditions, such as cataracts.
• Treatment for bleeding and bruising. If you or your child has a history of easy bruising or excessive bleeding, avoid aspirin and aspirin-containing products. In some cases, doctors may prescribe drugs that help the blood to clot.

• Treatment for lymphatic problems. Although lymphatic problems are a less common symptom, the many ways in which they can occur can make finding the problem and then treating it a challenge. Complications usually involve excess fluid that gets stored in various places in your body. Often the problems take care of themselves during childhood, but sometimes they don't show up until you're older.

  Chronic fluid retention in your feet and legs is rare, but if it happens, it's extremely important to take good care of your feet. Make sure you have shoes that fit well, and examine your feet regularly for any sores or skin problems. If problems develop, see your doctor.

  Sometimes fluid can collect in the space around your heart and lungs. If this happens, your doctor may want to insert a tube into your chest to drain the fluid. To prevent this problem, your doctor may suggest you modify your diet. Sometimes surgery is necessary if swelling around the heart and lungs persists.

• Genitourinary treatment. If your son has undescended testicles at birth, your doctor will likely refer you to an experienced surgeon to consider whether an injection of human chorionic gonadotrophin or surgery is appropriate. It's best for your child to receive such treatment before he enters school. Another common problem in males with Noonan syndrome is that their testicles don't function properly, in which case testosterone replacement is an option.

  If a urinary tract infection occurs, treatment is with antibiotics.

• Spinal treatment. Scoliosis often occurs in children with Noonan syndrome. Treatment options include bracing and surgery.
• Treating hearing problems. Have your child's hearing evaluated when he or she is an infant. Schedule repeat tests every year. If ear infections are a problem, prompt treatment may avoid hearing loss. In some cases of hearing loss, your child may need a hearing aid.

If you have a family history of Noonan syndrome, talk to your doctor and undergo genetic counseling before you have children. However, because many of the cases of this disease occur spontaneously, there's no way to prevent it.

If Noonan syndrome is detected early, it's possible that ongoing and comprehensive care may lessen some of its complications, such as heart disease.

A number of support groups are available for people with Noonan syndrome and their families. Talk to your doctor about finding a support group in your area. There are also good resources on the Internet that can direct you to local support groups and sources of information about this disease.