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Noonan Syndrome

Definition


Disease: Noonan Syndrome Noonan Syndrome
Category: Genetic Diseases
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Disease Definition:

The genetic disorder that hinders the normal development in different parts of the body is known as Noonan syndrome. some of the things that Noonan syndrome may cause in a child include:

 

  • Short stature
  • In some cases mental retardation
  • Unusual facial characteristics
  • Heart defects
  • Other physical problems


When a child inherits a copy of an affected gene from a parent, Noonan syndrome occurs. However, in some cases there may be no family history involved, and a child may have a spontaneous genetic mutation.


Controlling the symptoms and complications of Noonan syndrome is what treatment will focus on, because this disorder doesn't have a specific treatment. Moreover, short stature may be treated with growth hormone.

Work Group:


Prepared by: Scientific Section

Symptoms, Causes

Symptoms:

FACIAL FEATURES:

One of the key clinical features that help in the diagnosis of Noonan syndrome is the appearance of the child's face. The change that occurs on the features of the child depends on his/her age:


Early infancy:
When a child with Noonan syndrome is less than 1 month old, he/she will have a deep groove and wide peaks in the upper lip, a low hairline on the back of the head, low-set ears, a short neck and wide-set and down-slanting eyes.


Infancy:
An infant with Noonan syndrome may have a nose with a depressed root and a wide base and bulging tip, in addition to prominent eyes with a downward slant and thickened lids.


Childhood:
A child with Noonan syndrome usually has a lack of facial expressions.


Adolescence:
An adolescent with Noonan syndrome usually has a wide forehead that tapers to a pointed chin, prominent neck (trapezius) muscles or a long neck with webbed skin. The eyes become less prominent and the facial features become sharper.


Adulthood:
In an adult with Noonan syndrome, the crease that runs from the edge of the nose to the corner of the mouth will become larger, and the skin may become wrinkled and seem to be transparent.


HEART DISEASE:

Another one of the key signs and symptoms of Noonan syndrome is having congenital heart disease. This occurs in more than half of the people with Noonan syndrome. Noonan syndrome in children is usually discovered by pediatric cardiologists. Some of the most common types of congenital heart diseases that occur with this syndrome include:


Pulmonary valve stenosis:
In this disease, the pulmonary valve, which is the flap of tissue separating the lower right chamber (ventricle) of the heart from the artery that supplies blood to the lungs (pulmonary artery), becomes narrowed. This disease may be associated with other defects, or it may occur on its own. Pulmonary valve stenosis is the most common heart problem that occurs in people with Noonan syndrome.


Hypertrophic cardiomyopathy:
About 30% of people with Noonan syndrome have this disease. In hypertrophic cardiomyopathy, the heart muscle grows in an abnormal way or it becomes thickened.


Structural defects:
Structural heart defects are quite common in people with Noonan syndrome. Some of those defects may be a condition that causes the arteries that carry blood to the lungs for oxygen to become narrowed called pulmonary artery stenosis, or a condition in which there's a hole in the wall separating the two lower chambers of the heart called ventricular septal defect.


GROWTH PROBLEMS:

Although the weight of the child at birth will probably be normal, the child may have problems with feeding, causing poor weight gain until about 18 months. The growth spurt that usually occurs during adolescence will be delayed in a child with Noonan syndrome, and the child may continue growing even when he/she reaches 20s. Adults with Noonan syndrome usually have short stature, and only about one-third of them have normal height.


LYMPHATIC PROBLEMS:

The lymphatic system, which drains excess fluid from the body and helps fight infection, may be affected by Noonan syndrome. lymphedema (excess fluid) on the back of the hands or top of the feet is one of the most common problems with the lymphatic system. In general, these problems may be either widespread, or they may affect a particular area of the body they may also show up before or after birth.


MUSCULOSKELETAL ISSUES:

People with Noonan syndrome may have low muscle tone, short neck with extra folds of skin, wide-set nipples and a chest that is irregularly shaped, usually with either a raised sternum (pectus carinatum) or with a sunken sternum (pectus excavatum).


EYE PROBLEMS:

Another one of the key features of Noonan syndrome is the differences in the shape and size of the eyes. In most cases, the color of the iris is pale blue or green. Almost all people with Noonan syndrome have abnormalities in their eyes and eyelids. Some of the common eye problems that occur in people with Noonan syndrome include:

 

  • Hypermetropia
  • Problems with the nerves of the eyes
  • Strabismus or crossed eyes, which are problems with the eye muscles
  • Nearsightedness (myopia) and astigmatism, which are refractive problems
  • Nystagmus, which is the rapid movement of the eyeballs


SKIN PROBLEMS:

People with Noonan syndrome may have a tendency to develop thick scars after surgery. In most cases, people with this syndrome have sparse hair, or curly and coarse hair. Additionally, they may develop different problems affecting the color and texture of their skin.


BLEEDING:

Most people with Noonan syndrome have had abnormal bleeding or bruising at some point in their lives. In some cases, this problem may not be discovered until someone with Noonan syndrome undergoes surgery and experiences hemorrhage.


LEARNING DISABILITIES:

About one-third of children with Noonan syndrome may have mild mental retardation. Significant mental retardation is quite uncommon. Children with Noonan syndrome usually get along without any difficulty in school and go to college.


GENITAL AND KIDNEY PROBLEMS:

Problems with the genitals and kidneys may occur in people with Noonan syndrome, particularly in boys. Although most girls with Noonan syndrome develop normal fertility, but both boys and girls may experience delayed puberty. Additionally, because Noonan syndrome in males causes undescended testicles, they may not develop normal fertility.

The kidney problems caused by Noonan syndrome are usually mild and affect only a small number of people.


If a person suspects that they or their children may have Noonan syndrome, a primary care physician should be consulted, in which case the doctor may refer them to a geneticist or a cardiologist. The signs and symptoms of Noonan syndrome may be subtle, but the disorder can be discovered with molecular genetic testing. Prenatal tests are also available if an unborn child has a risk of developing this syndrome due to family history.

Causes:

A mutation in a particular gene is the cause of Noonan syndrome. So far, four genes that can cause Noonan syndrome have been identified. As mentioned before, this disease may be the result of inheriting a mutation of genes from a parent (autosomal dominant), or it may be the result of a new mutation in children who don't have a genetic predisposition for this syndrome. Children who have a parent with this syndrome have a 50% chance of developing it themselves. Only about 0.001 to 0.0004% of newborns are affected by Noonan syndrome, meaning that this disease is very rare.


The four identified genes that may cause Noonan syndrome if they mutate are:


PTPN11 gene:
The mutation that occurs in this gene is responsible for almost half the cases of Noonan syndrome.


SOS1 gene:
The mutation that occurs in this gene is responsible for about 20% of the cases of Noonan syndrome.


RAF1 gene:
The mutation that occurs in this gene is responsible for about 15% of the cases of Noonan syndrome.


KRAS gene:
The mutation that occurs in this gene causes a more severe form of Noonan syndrome, and is responsible for about 5 to 10% of all cases.


Constantly active proteins are produced by these genes due to their defects. The normal process of cell growth and division will be disrupted due to the constant activity of the proteins because these genes participate in the formation of many tissues throughout the body.


Noonan syndrome may also be caused by other undiscovered genes, because not always do people with Noonan syndrome have mutations in the above mentioned genes. Additionally, people who have a mutation in the neurofibromin 1 gene produce a protein that helps to keep cells from growing too fast or in an uncontrolled way. People with this mutation have Noonan syndrome along with a condition called neurofibromatosis 1.

Complications

Complications:

The medical specialists who are handling a case of Noonan syndrome should handle the various symptoms of this syndrome in a coordinated way.


Some of the complications that may need special attention include:


Bleeding and bruising:
The excessive bleeding and bruising caused by Noonan syndrome may cause difficulties during surgery or dental work. Aspirin thins the blood; because of this, people with Noonan syndrome should avoid using it. Children in general should avoid aspirin because it’s associated with a very serious condition called Reye’s syndrome.


Developmental issues:
A child may have difficulty with organization and spatial sense if he/she has developmental issues. In some cases, in order to address the learning and educational needs of the child, a special plan of action may be needed.


Genital and urinary tract complications:
The structural abnormalities in the kidneys that are caused by Noonan syndrome may increase the risk of urinary tract infections. Additionally, because Noonan syndrome causes undescended testicles (cryptorchidism), males who have this syndrome may have a low sperm count and other fertility problems.


Complications from lymphatic problems:
In some cases, chest tube drainage may be needed in case fluid collects in the cavity around the heart and lungs. Weight loss, infection or other complications may result in case the draining is prolonged or repeated.

Treatments:

Usually, the type and severity of the symptoms and complications of Noonan syndrome will determine the treatment.
Some of the recommended treatment approaches may include:


Heart treatment:
Some drugs might be effective in treating certain heart problems. Should there be any problem with the patient’s heart, surgery may be necessary. The doctor may recommend periodical evaluation for the heart function. Moreover, the dentist may recommend the preventive use of antibiotics before any dental cleaning or surgery.


Vision treatments:
People with Noonan syndrome need regular eye exams because they usually have vision problems. Glasses can correct most eye issues. However, in the case of cataracts, surgery will be needed.


Treating low growth rate:
In order to make sure that a child with Noonan syndrome is growing at a normal rate, the child should be measured at every routine well-child visit, as well as every six to twelve months, because this syndrome hinders growth. Children with Noonan syndrome  may also end up having malnutrition due to the fact that this syndrome causes eating difficulties. The child’s hormone levels, blood chemistry, bone growth and thyroid function should also be checked. Growth hormone therapy may be an option in case the child has insufficient growth hormone levels.


Treatment of genital and urinary tract problems:
In case a child has undescended testicles at birth, to decide whether surgery is appropriate or an injection of human chorionic gonadotrophin, the parents are likely to be referred to an experienced surgeon. A child should receive this treatment before starting school. Additionally, testosterone replacement may treat another common problem in males with this syndrome, which is when their testicles don't function properly.
Antibiotics are usually used to treat urinary tract infections.


Addressing learning disabilities:
Noonan syndrome may cause a variety of mental and behavioral issues. The symptoms of these conditions, which are usually mild, can be managed. Infant stimulation programs may help if a child’s developmental delays have been discovered early. Sometimes, individualized teaching or special education may be needed. In addition to all this, physical and speech therapies may help in different ways.


Treatment for bleeding and bruising:
Sometimes, a person with Noonan syndrome may be prescribed medications that help the blood clot. Acetylsalicylic acid (Aspirin) should be avoided by children with a history of easy bruising or excessive bleeding.


Treatment for lymphatic problems:
Finding problems in the lymphatic system and then treating it could be quite difficult because of the way in which they appear. The storage of excess fluid in various parts of the body is one of the complications. Additionally, to prevent the collection of fluid around the heart and lungs, the patient may be recommended to modify his/her diet. However, if fluids do collect around the heart and lungs, a tube will be inserted into the chest of the person in order to drain the fluid. In case the swelling around the heart and lungs persists, surgery will be necessary.

Prognosis:

Not Available

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