What is Noonan syndrome?

A 12-year-old female with Noonan syndrome. Typical webbed neck. Double structural curve with rib deformity.Have you come across a child or an adult with unusual facial features such as sagging and drooping eyelids, a very broad or webbed neck (excessive folds of neck skin), short stature, abnormally shaped and low-set ears, and strikingly blue or bluish green eyes? Well, these people are victims of a rare genetic disorder known as Noonan Syndrome or Turner-like syndrome!

Did You Know?

  • 1 child in every 1,000 children to 1 in every 2500 children is born with this syndrome.
  • Every day a child is born with it.
  • It is usually inherited by the children from their parents in an autosomal dominant mode of inheritance. This means any one parent having the mutated (defective) gene in each cell can lead to the development of this syndrome in their child by passing it to him/her.

The oldest known case of Noonan syndrome, described in 1883

Typical Symptoms:

Following is the list of symptoms associated with Noonan Syndrome.

  • Short stature.
  • Heart condition such as congenital heart disease at birth.
  • Wide, down-slanting eyes that are either pale blue or bluish green in color.
  • Short neck.
  • Low hairline at the back of the neck.
  • A deep groove in the region between the nose and the mouth.
  • Backwardly rotated low-set ears.
  • Webbing of the neck or excess skin folds in the neck region.
  • Improper teeth alignment.
  • High arched palate or a high arch in the roof of the mouth.
  • Micrognathia or a small lower jaw.
  • Pectus excavatum or a sunken chest, or pectus carinatum or a protruding chest.
  • Pulmonary Valve Stenosis, a condition in which the heart valve that regulates the flow of blood from the heart to the lungs becomes narrowed.
  • Hypertrophic Cardiomyopathy, a condition in which the heart muscles thicken forcing the heart to work harder to pump the blood.
  • Arterial Septal Defect, a condition characterized by the presence of a hole in between the top 2 heart chambers.
  • Ventricular Septal Defect, a heart condition characterized by the presence of a hole in between the bottom 2 chambers of the heart.
  • Bleeding disorders such as nosebleeds, excessive bruising, prolonged and continuous bleeding after a surgery or an injury.
  • Women with bleeding disorders may experience heavy bleeding during childbirth or menstruation.
  • Adolescent boys may experience a delay in reaching puberty. Decreased puberty growth spurt is seen in them.
  • Cryptorchidism or undescended testicles (testicles do not descend into the scrotum or the bag that holds testicles) in boys which may lead to infertility in the later stages of life.
  • Small penis.
  • Some children may need special education due to learning disabilities.
  • Hearing or vision problems may be seen in some affected individuals.
  • Newborns with this syndrome may have puffy feet and hands due to the accumulation of fluid, a condition known as lymphedema.
  • A mild mental retardation is seen in nearly 25% of the affected people.
  • Almost 95% of the affected people may have strabismus or crossed eyes, a condition of eyes in which both the eyes look at different objects at the same time because they are not lined up in the same direction.
  • Children may have feeding problems. They may face sucking problems due to weak mouth muscles.
  • Unusually round shoulders.

Genes Involved in Noonan Syndrome:

Four genes have been associated with the development of this syndrome, RADF1, PTPN11, KRAS and SOS1. Mutations in any one of these genes may lead to this condition.

  • Nearly 50% of the people with this syndrome have mutations in PTPN11 gene.
  • Mutations in SOS1 gene lead to the development of this condition in 10% to 15% of the affected population.
  • RADF1 gene mutations account for 5% to 10% of the affected cases.
  • Finally, KRAS gene mutations are seen in as low as 2% of the people with this syndrome.

All these genes are very crucial for the production of major proteins in the body required for several important tissue functions in the body. Cell movement, cell division/ proliferation and cell differentiation are the 3 major activities that require the help of these proteins.

Usually as the cells signal, the proteins switch on/off as per the requirement of the cell. Mutations in any of these genes lead to the uninterrupted protein activity which is an abnormal scenario. Due to this continuous activity of the proteins, disruption to the cell systems that regulate cell division and growth occurs leading to the development of facial and other features that are typically seen in Noonan Syndrome patients.

Detecting Noonan Syndrome:

  • The very first indication is the presence of epicanthal folds or the extra skin folds just above the eyes near the nose.
  • In order to find out the presence of mutations in any of the above-mentioned 4 genes, genetic testing is mandatory.
  • Signs of congenital heart disease like pulmonary stenosis.
  • Platelet count is checked by performing blood tests. This may reveal the signs of bleeding.
  • Symptomatic diagnostic tests such as echocardiogram or chest X-ray in cases of heart disease, hearing tests in people who complain of hearing impairment may be performed.

Can Noonan Syndrome Be Treated?

Genotropin - Growth Hormone

Well, this is a difficult question to answer as the symptoms are not limited to one single part of the human body.

Doctors usually treat the condition symptomatically just like the diagnosis is confirmed based on symptoms.

In some individuals’ growth hormone worked wonders against short stature.

If the syndrome runs in your family, make sure to get genetic counseling done before you plan to have children!

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