Heart Conditions and Diagnoses

Noonan Syndrome

Features, Heart Problems and Inheritance

Explanation | Features | Heart Problems | Other Problems | Inheritance

What is Noonan syndrome?

Noonan syndrome is a genetic disorder originally described by Noonan and Ehmke in 1963. The majority of early patients recognized to have this syndrome were boys, but it is now clear that girls are equally affected.

Noonan syndrome occurs in about 1/1,000 to 1/2,500 live births. The actual genetic abnormality has not yet been discovered.

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Noonan syndrome features found in infants

Babies with Noonan syndrome may be diagnosed in infancy because of unusual facial features, including closely spaced and down-slanted eyes and ears that are positioned low on the head and rotated to the back.

The vertical groove lying in the space between the upper lip and nose is deep and the jaw is small.

There is excess neck skin and the hairline is low on the back of the neck.

As the baby grows, the head appears larger than normal with prominent eyes and depression of the top of the nose. The face becomes less triangular in appearance.

The baby's birth weight and birth length are usually normal, but after birth the patient's growth is delayed, with growth usually following along the 3rd percentile (i.e., the Noonan Syndrome patient is taller and heavier than only 3 percent of children his or her age).

Do the features of Noonan syndrome change as the patient grows up?

In some young adults, the eyes become less prominent.

Because the patient's neck is relatively short, the "webbed" appearance of the neck is exaggerated.

The patient's skin may be wrinkled or transparent-appearing.

The hairline in the front is high and the hair itself is usually described as curly or wooly in older children and teens.

How specific are the physical features of Noonan syndrome?

The clinical features of Noonan syndrome can overlap with a number of other syndromes. In girls suspected of having Noonan syndrome, a chromosomal analysis will often be performed to rule out Turner Syndrome.

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Heart in Noonan syndrome patients

Heart problems occur in about two-thirds of Noonan syndrome patients, with the most common problem being an abnormal narrowing and often thickening of the pulmonary valve.

Other relatively common heart defects are atrial septal defect (ASDs), ventricular septal defect (VSDs), patent ductus arteriosus (PDA), and abnormal thickening of the heart muscle itself (hypertrophic cardiomyopathy). Problems with the pulmonary valve can be minor, requiring no intervention.

If the narrowing is significant it may require a procedure such as cardiac catheterization to dilate the narrowed area with a balloon.

Unfortunately, children with Noonan's and pulmonary stenosis often have multiple levels of narrowing which cannot be dilated and will require heart surgery.

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Medical problems associated with Noonan syndrome

Children with Noonan syndrome may have medical problems outside of the heart. Mild mental retardation is present in 35 percent of patients.

An important feature of Noonan syndrome is an unexplained tendency to bleed that should be taken into consideration when procedures likely to cause bleeding are planned.

The adolescent growth spurt is often blunted or delayed and 60 percent of males have undescended testes. In addition to delay in growth, sexual development is variable and may also be delayed.

Adult women with Noonan syndrome are usually able to have children but carry a 50 percent risk of passing the disease to their children.

Skeletal malformations are common. About 70 percent of patients with Noonan syndrome have abnormalities of the rib cage such as "pigeon breast" (pectus carinatum) or a sunken breastbone (pectus excavatum).

Curvature of the spine (scoliosis) is an early important feature in 40 percent of patients, with half of the spine curves present by age 2 and the remaining 50 percent by age 5.

Other abnormalities of the spine (the individual vertebrae) and of the arms and feet can also occur

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Inheritance of Noonan syndrome

Some experts believe that most cases of Noonan syndrome are sporadic (not inherited), although 30 percent to 50 percent may be inherited.

Since the diagnosis of Noonan syndrome in patients without heart disease can be difficult, the actual percentage of inherited cases may be higher than estimated.

It appears that the majority of inherited cases come from the mother, suggesting that men with Noonan syndrome are infertile. Some think that the risk of recurrence of the disease in siblings of the affected patient is approximately 50 percent, with an approximately 50 percent risk of a parent transmitting Noonan syndrome to his or her offspring.