What is Noonan syndrome?

Noonan syndrome is a genetic (inherited) condition that causes symptoms and problems in several parts of the body, including the head, heart and limbs (hands and feet).

Noonan syndrome can cause distinctive facial features, including a prominent forehead. Heart problems in patients with Noonan syndrome include congenital (the child is born with it) valve problems as well as thickening of the heart muscles.

Who is likely to have Noonan syndrome?

Anyone can be born with Noonan syndrome. The condition is more common among people whose parents have Noonan syndrome

Noonan syndrome occurs in 1 of every 1,000-2,500 people.

What causes Noonan syndrome?

Noonan syndrome occurs because of certain mutations (changes) on specific genes inherited from a person’s parents, including the genes PTPN11, SOS1, RAF1, RIT1, and KRAS. Approximately 50 percent of people with Noonan syndrome have a parent who also has the condition.

These genetic changes can also occur randomly. In 60 percent of cases, Noonan syndrome occurs from spontaneous genetic mutations that have no known cause.

What are the signs and symptoms of Noonan syndrome?

Noonan syndrome causes a variety of symptoms and problems, depending on which body systems or structures are affected:

Head and neck

  • Large head with a deep groove in the middle of the upper lip, small jaw, improperly aligned teeth, and ears pointed backward
  • Blue or bluish-green eyes that are widely set, turn in or out (strabismus), or have unusually thick or drooping eyelids (ptosis)
  • Webbing of the neck and a low hairline on the back of the neck


  • Pulmonary stenosis (a blockage of blood flow from the heart to the lungs), atrial septal defect (an opening between the upper heart chambers), and hypertrophic cardiomyopathy (thickening of the heart muscle)


  • Bulging finger pads or toes, misshapen or discolored nails, and changes in hair texture

Other problems/symptoms

  • Lymphedema (a buildup of fluid that causes swollen hands or feet)
  • In infants, failure to thrive (feeding problems and failure to gain weight and grow)
  • Short stature
  • Scoliosis (abnormal curvature of the spine)
  • Pectus excavatum, an abnormal development of the rib cage in which the sternum (breastbone) grows inward, resulting in an indentation of the chest wall
  • Delayed puberty, undescended testes, or infertility (inability to produce children)
  • Intellectual disabilities
  • Vision problems or hearing loss
  • Bleeding problems

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