Noonan Syndrome Diagnosis

Noonan syndrome is a common inherited disorder of cell growth affecting both males and females and characterized by atypical facial features, short stature, heart defects, bleeding problems, chest wall abnormalities, and other signs and symptoms. Noonan syndrome occurs in about 1 in 2,000 births. It was first identified and recognized in the early 1960s and is to be distinguished from Turner syndrome, an inherited chromosomal abnormality with similar features affecting only females. The diagnosis is made through observation and using a scoring system that evaluates common features of the syndrome. Many children with Noonan syndrome also have a short "webbed" neck and a low hairline. Most are born normal sized, but develop into below average height adults. Males and females can be diagnosed with Noonan syndrome, but typically males are affected more seriously, including with issues such as delayed puberty and infertility. There is no racial or ethnic predisposition and Noonan syndrome occurs at the same rate in all individuals.

Most children diagnosed with Noonan syndrome have normal intelligence, though up to 25% percent may have some developmental disability. Most children with Noonan syndrome develop and function normally as adults; however, they all should be fully evaluated to determine the severity of their symptoms and defects and to determine what sort of interventions might be needed to keep them healthy. The most common cause of premature death or illness is related to the type and severity of the heart defect. Some known issues that need to be addressed include:

  1. Genetic evaluation and testing to confirm the diagnosis (scoring system for Noonan syndrome)
  2. Complete evaluation of the heart (most commonly a pulmonary valve defect)
  3. Genital examination (undescended testes in males)
  4. Feeding history (many young infants have poor feeding and decreased muscle tone early on)
  5. Developmental evaluation (motor and intellectual)
  6. Bruising history (some bleeding abnormalities actually resolve over time)
  7. Physical growth (some children may benefit from growth hormone therapy)

Many patients with Noonan syndrome are not all easily diagnosed at birth, because the typical features may not be apparent until they enter childhood. In addition, older adults with Noonan syndrome may also lose the typical appearance. Overall the prognosis for those individuals with Noonan syndrome is very good, especially if they have minimal heart abnormalities and a normal intellect. For these individuals, however, genetic counseling prior to family planning is extremely important since only a single copy of the gene from either parent is necessary and sufficient to cause the disorder. Noonan syndrome frequently occurs sporadically (meaning there is no family history) due to a number of identified mutations in different genes, which explains why there is significant variability in the severity of the signs and symptoms seen in different patients with Noonan syndrome.

Medically reviewed by Margaret Walsh, MD; American Board of Pediatrics


"Noonan syndrome." Genetic and Rare Diseases Information Center. 1 Oct. 2013.

"Noonan syndrome." Genetics Home Reference. Mar. 2011.