|Classification and external resources|
A 12-year-old female with Noonan syndrome. Typical webbed neck. Double structural curve with rib deformity.
Noonan syndrome (NS) is a relatively common autosomal dominant congenital disorder that affects both males and females equally:550. It used to be referred to as the male version of Turner's syndrome (and is still sometimes described in this way); however, the genetic causes of Noonan syndrome and Turner syndrome are distinct. The principal features include congenital heart defect (typically pulmonary valve stenosis) also ASD, hypertrophic cardiomyopathy, short stature, learning problems, pectus excavatum, impaired blood clotting, and a characteristic configuration of facial features including a webbed neck and a flat nose bridge. The syndrome is named after Dr. Jacqueline Noonan. It is a RASopathy, as the syndrome is in the family of RAS-MAPK pathway disorders.
It is believed that between approximately 1 in 1,000 and 1 in 2,500 children worldwide are born with NS. It is one of the most common genetic syndromes associated with congenital heart disease, similar in frequency to Down syndrome. However, the range and severity of features can vary greatly in patients with NS. Therefore, the syndrome is not always identified at an early age.
Often called a "hidden" condition, the person affected may have no obvious casual signs to the onlooker, but the problems may be many and complex. The most prevalent (common) signs are highlighted in bold with frequency listed in parentheses.
By organ system 
2/3 of people have one of the following heart defects:
- Pulmonary Valvular Stenosis —(50%)
- Septal defects: atrial —(10%) or ventricular —(less common)
- Heart murmur
Gastrointestinal system 
- Failure to thrive as an infant
- Decreased appetite
- Digestive problems
- Frequent or forceful vomiting
- Swallowing difficulties
Genito-urinary system 
- Cryptorchidism (undescended testicles) —
Lymphatic system 
- Posterior cervical hygroma (webbed neck)
- Lymphedema (build-up of body fluid due to poor functioning of the lymphatic system)
- Easy bruising
- Amegakaryocytic Thrombocytopenia (low platelet count)
- Blood Clotting Disorders
- Von Willebrand disease
- Prolonged activated partial thromboplastin time
- Partial deficiency of Factor VIII:C
- Partial deficiency of Factor XI:C
- Partial deficiency of Factor XII:C
- Combined Coagulation deficiencies
- Many people affected by Noonan Syndrome suffer from joint pain or muscle pain, particularly in adulthood, which varies in severity. Recent research confirms this, however, the etiology is unknown, therefore more extensive research is required.
Arnold-Chiari Malformation (Type 1) has been noted in some patients with Noonan Syndrome
By physical appearance 
Stature and posture 
- Short stature
- Cervical (neck) spine fusion
- Prominence of breast bone (pectus carinatum)
- Depression of breast bone (pectus excavatum)
- Joint contractures or tightness
- Joint hyperextensibility or looseness
- Growth retardation
- Winging of the scapula
- Hypotonia (low muscle tone)
- Lordosis (increased hollow in the back) due to poor stomach muscle tone
- Excess skin on the back of the neck
- Low hairline at the nape of the neck
- High hairline at the front of the head
- Large head
- Triangular face shape
- Broad forehead
- Short neck, webbed neck, posterior cervical
- Curly hair
- Widely set eyes (hypertelorism) —(95%)
- Drooping of the eyelids (ptosis (eyelid))
- Epicanthal folds (extra fold of skin at the inner corner of the eye)
- Proptosis (bulging eyes)
- Refractive visual errors
- Inward or outward turning of the eyes (strabismus)
- Nystagmus - jerking movement of the eyes
- Small, upturned nose
Ears and hearing 
- Low set ears —(over 90%)
- Backward rotated ears —(over 90%)
- Thick helix of ear (outer rim) —(over 90%)
- Incomplete folding of ears
- Chronic Otitis media (ear infections)
Mouth and speech 
- Deeply grooved philtrum (top lip line) —(over 90%)
- Micrognathia (undersized lower jaw)
- High Arched palate
- Dental problems
- Articulation Difficulties
- Poor tongue control
- Bluntly ended fingers
- Extra padding on fingers and toes
- Edema of the back of hands and tops of feet
- Cubitus valgus (elbow deformity: with abnormal turning-in)
- Lymphedema (swelling of the extremities)
- Keloid formation
- Hyperkeratosis - overdevelopment of outer skin layer
- Pigmented nevi (birthmark)
Recurrence in siblings and apparent transmission from parent to child has long suggested a genetic defect with autosomal dominant inheritance and variable expression. Mutations in the Ras/mitogen activated protein kinase signaling pathways are known to be responsible for ~70% of NS cases.
A person with NS has up to a 50% chance of transmitting it to a child. The fact that an affected parent is not always identified for children with NS suggests several possibilities:
- manifestations are variably expressed and could be so subtle as to go unrecognized (variable expressivity)
- a high proportion of cases represent new, sporadic mutations or
- Noonan syndrome is heterogeneous, comprising more than one similar condition of differing cause, some not inherited.
|NS1||163950||PTPN11||In most of the families with multiple affected members, NS maps to chromosome 12q24.1. In 2001, it was reported that approximately half of a group of patients with Noonan syndrome carried a mutation of the PTPN11 gene at that location, which encodes protein tyrosine phosphatase SHP-2. The SHP2 protein is a component of several intracellular signal transduction pathways involved in embryonic development that modulate cell division, differentiation, and migration, including that mediated by the epidermal growth factor receptor. The latter pathway is important in the formation of the cardiac semilunar valves.
Chromosomal abnormalities, such as a duplication of chromosome region 12q24 encompassing gene PTPN11 can result in an apparent Noonan syndrome.
|NS2||605275||unknown (autosomal recessive)|
|NS3||609942||KRAS||Additional mutations in KRAS  genes have been reported to cause Noonan syndrome in a smaller percentage of individuals with the syndrome.|
|NS4||610733||SOS1||It has recently been shown that activating mutations in SOS1 also give rise to NS. Shp2 and SOS1 both have roles as positive regulators of the Ras/MAP kinase pathway suggesting that dysregulation of this pathway may play a major role in the genesis of this syndrome.|
|NS5||611553||RAF1||Additional mutations in RAF1 genes have been reported to cause Noonan syndrome in a smaller percentage of individuals with the syndrome.|
Despite identification of six causative genes, the diagnosis of Noonan syndrome is still based on clinical features. In other words, it is made when a physician feels that a patient has enough of the features to warrant the label indicating association.
The following genes are known to cause NS with the percentage of cases in brackets. PTPN11 (50%) RAF1 (3-17%) SOS1 (10%), KRAS (1%) , NRAS (unknwown) or BRAF (unknown).
An absence of a mutation will not exclude the diagnosis as there are more as yet undiscovered genes that cause NS. The principal values of making such a diagnosis are that it guides additional medical and developmental evaluations, it excludes other possible explanations for the features, and it allows more accurate recurrence risk estimates. With more genotype-phenotype correlation studies being performed, a positive genetic diagnosis, will help the clinician to be aware of possible anomalies specific to that certain gene mutation, for example, there is an increase in hypotrophic cardiomyopathy in patients with a mutation on the KRAS gene, and patients with a mutation on PTPN11 have an increased risk of Juvenile myelomonocytic leukemia. In the future, there will be scope for targeted management of Noonan Syndrome, depending on what genetic mutation the patient has.
Jacqueline Noonan was practicing as a pediatric cardiologist at the University of Iowa when she noticed that children with a rare type of heart defect, valvular pulmonary stenosis, often had a characteristic physical appearance with short stature, webbed neck, wide spaced eyes, and low-set ears. Both boys and girls were affected. Even though these characteristics were sometimes seen running in families, chromosomes appeared grossly normal. She studied 833 patients at the congenital heart disease clinic, looking for other congenital abnormalities, and in 1962 presented a paper: "Associated non-cardiac malformations in children with congenital heart disease". This described 9 children who in addition to congenital heart disease had characteristic faces, chest deformities and short stature. Both males and females were found to be similarly affected, and the chromosomes were apparently normal.
Dr. John Opitz, a former student of Dr. Noonan, first began to call the condition "Noonan Syndrome" when he saw children who looked like those whom Dr. Noonan had described. Dr. Noonan later produced a paper entitled "Hypertelorism with Turner Phenotype", and in 1971 at the Symposium of Cardiovascular defects, the name 'Noonan Syndrome' became officially recognized.
See also 
- Turner syndrome — a different disorder which is often confused with Noonan syndrome because of several physical features that they have in common.
- Fetal alcohol syndrome — another disorder that is sometimes confused with Noonan syndrome because of some common facial features and mental retardation
- Leopard syndrome— A related disorder caused by mutations in PTPN11 that are catalytically inactivating.
- Cardiofaciocutaneous syndrome — A related disorder which also affects genes encoding elements of the Ras/MAP kinase pathway.
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|Wikimedia Commons has media related to: Noonan syndrome|
- Noonan Syndrome Community (International) - Offers Support, Information, & Raises Funding For Research - Visit www.noonansyndrome.me for details!
- Noonan Syndrome Is a RASopathy - Visit The RASopathies Foundation To Learn More! www.teamrasopathies.org
- Noonan syndrome at the Open Directory Project
- GeneReviews: Noonan syndrome
- - The Noonan Syndrome Association is a UK charity for families and individuals affected by Noonan Syndrome