Noonan Syndrome

What is Noonan Syndrome?

Noonan Syndrome is a disorder caused by a genetic mutation that causes various parts of the patient’s body to develop abnormally. The condition occurs when a parent passes on an affected gene to their child that produces constantly active proteins, leading to a disruption in the process of normal cell division and growth.

Science currently knows of eight genes in which a mutation can cause the disorder. In some cases, there is no family history and the mutation is spontaneous.

What are the Symptoms of Noonan Syndrome?

One of the main indications of Noonan syndrome is the abnormal development of the person’s face, which varies at different ages. Newborn babies generally have low-set ears, slanting or wide-set eyes, and a short neck, among other features.

Infants can develop thickened eyelids as their eyes become more prominent, while a young child’s face may seem devoid of expression. A teenager’s facial features tend to sharpen, and an adult’s skin could appear transparent and become wrinkled.

Other common symptoms and complications that result from Noonan syndrome include:

  • Congenital heart disease
  • Thickened heart muscle
  • Heart valve disorders
  • Heart structural defects
  • Growth issues in childhood
  • Short stature in adults
  • Musculoskeletal issues
  • Eye abnormalities
  • Learning disabilities
  • Lymphatic disorders
  • Bleeding
  • Easy bruising
  • Urinary tract complications
  • Skin conditions
  • Kidney problems
  • Delayed puberty
  • Genital abnormalities

Noonan Syndrome Causes

Noonan syndrome is primarily caused by a defective gene, indicating that the condition is inherited from one’s parents. Where some external factors may produce genetic abnormalities, that doesn’t seem to be the case with Noonan syndrome. There’s no evidence to suggest environmental factors, diet, lifestyle, or exposure to radiation plays a part in mutating the genes. The genes affected are the PTPN11, SOS1, RIT1, RAF1, and KRAS genes.

In rare instances, about 1 in 5 cases, there is no known gene abnormality causing Noonan syndrome. Meanwhile, autosomal dominant patterns are responsible for the development of the disease in 30-75% of cases. In other words, one parent will have to carry the faulty gene and pass it onto the child, who will then have a 50% chance of developing Noonan syndrome. The parent carrying the defective gene will also have the disease, though symptoms may be mild enough that it could go undiagnosed.

Even in cases where a couple has already had one child with Noonan syndrome, there is still a 50% chance that second or third child will carry the defective gene.

How is Noonan Syndrome Treated?

There is no way to cure or prevent Noonan syndrome, so treatment is focused on relieving the resulting complications. Therapies will vary depending on severity and the nature of symptoms.

Heart problems can be controlled through medications and, if necessary, surgery. Children with a slow growth rate may be given growth hormone therapy. Learning disabilities can be improved through various speech and physical therapies, while patients who bleed or bruise easily should avoid aspirin. Glasses are often sufficient for vision issues, although conditions like cataracts might require surgery.

Noonan Syndrome Prevention

There are two factors that make preventing Noonan syndrome currently impossible. First, the condition is inherited with no known external factors affecting its development. Making it even harder to predict, there are some instances in which Noonan syndrome appears spontaneously, meaning it hasn’t been genetically passed on from parents to child.

In cases where there is a known family history of Noonan syndrome, it’s recommended that couples hoping to have children speak to their doctor about genetic counseling. This may help determine if the defective genes are present in either parent through molecular genetic testing.

If Noonan syndrome is detected early, comprehensive treatment may decrease the risk of developing complications. Chiefly among them is heart disease.

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Last Reviewed:
October 07, 2016
Last Updated:
January 25, 2018