|Specialty||Medical genetics, pediatrics|
Noonan syndrome (NS) is a relatively common autosomal dominant congenital disorder and is named after Jacqueline Noonan, a pediatric cardiologist. It used to be referred to as a male version of Turner's syndrome; however, the genetic causes of Noonan syndrome are distinct from Turner syndrome and both males and females are affected. The principal features include congenital heart defect (typically pulmonary valve stenosis with dysplastic pulmonary valve also atrial septal defect and 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. NS is a RASopathy, and is one of several disorders that are caused by a disruption of RAS-MAPK signaling pathway.
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.
- There have been few reports of patients with Noonan syndrome who have subsequently suffered from Malignant Hyperthermia (MH). However Noonan's syndrome is not associated with MH. Only King-Denborough syndrome and central core disease are associated with MH. King-Denborough syndrome has been linked to a mutation on chromosome 19 located near the gene that encodes the ryanodine receptor whereas Noonan syndrome is associated with a mutation on chromosome 12.
- Some individuals with NS have been reported to develop respiratory depression from narcotics given during and after surgery, which has sometimes required cardiac resuscitation. Impaired anesthetic clearance in the 24–48 hours after surgery has also been reported.
Up to ~85% of people with NS have one of the following heart defects:
- Restrictive lung function has been reported in some patients
- Cryptorchidism (undescended testicles)
- Motor development delay/delayed milestones
- Learning disabilities
- Speech-language pathology
- Autism, pervasive developmental disorder
- Frequent illnesses, doctor appointments, pain, headaches and fatigue are a few things that can affect school attendance and performance.
- Despite the various possible developmental/learning issues that can be seen in NS, there are Noonan Syndrome patients that have advanced degrees, including at least two that have become attorneys. Source Noonan Syndrome Foundation
- Neuropsychological testing is recommended to find strengths and challenges to tailor support needed for school, career.
- Educational customization such as an Individualized Education Program plan or a Section 504 plan is sometimes needed for school-aged children.
- Speech therapy if there are speech and articulation issues
- Physical therapy and occupational therapy for gross and fine motor delays
- Hypotonia and motor difficulties often impact handwriting. Accommodations for lessening handwriting demands will improve performance and save long-term hand function.
- Bleeding disorders
- 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
- Platelet dysfunction
- Combined coagulation defects
- Imbalance of Plasminogen Activator Inhibitor Type-1 (PAI-1) and Tissue Plasminogen Activator (t-PA) Activity.
- Joint pain or muscle pain especially in adults, which can vary in severity
- Undifferentiated Connective Tissue Disorders
- Prominence of breast bone (pectus carinatum)
- Depression of breast bone (pectus excavatum)
- Joint contractures (tightness)
- Joint hypermobility (looseness)
- Winging of the scapula
- Hypotonia (low muscle tone)
- Hypermobility syndrome
- Lordosis (increased hollow in the back) due to poor stomach muscle tone
- Short stature Growth Hormone (GH) sometimes combined with IGF-1 (or as an alternative, IGF-1 as a stand-alone could be used as stated in cited paper) can be used to achieve an increased height/final height quicker.
- 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
- Small, upturned nose
Ears and hearing
- Low-set ears (in over 90%)
- Backward-rotated ears (over 90%)
- Thick helix (outer rim) of ear(over 90%)
- Incomplete folding of ears
- Chronic otitis media (ear infections)
- Hearing loss
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
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 their offspring. The fact that an affected parent is not always identified for children with NS suggests several possibilities:
- Manifestations could be so subtle as to go unrecognized (variable expressivity)
- NS is heterogeneous, comprising more than one similar condition of differing causes, and some of these may not be inherited.
- A high proportion of cases may represent new, sporadic mutations.
|Type||Online Mendelian Inheritance in Man database||Gene||Year found||Locus||% of cases||Description||Refs.|
|NS1||163950||PTPN11||2001||12q24.1||50%||The PTPN11 gene encodes the protein tyrosine phosphatase SHP-2. This protein is a component of several intracellular signal transduction pathways involved in embryonic development that modulate cell division, differentiation, and migration, including one mediated by the epidermal growth factor receptor, which is important in the formation of the semilunar heart valves.
Duplication of the chromosome region containing PTPN11 can also result in NS.
|NS2||605275||Unknown; autosomal recessive|
|NS4||610733||SOS1||2006||2p21||10%||Activating mutations in SOS1 can give rise to NS. SHP-2 and SOS1 positively regulate the Ras/MAP kinase pathway, suggesting that its dysregulation mediates NS development.|
NS can be confirmed genetically by the presence of any of the known mutations listed above. However, despite identification of fourteen causative genes, the absence of a known mutation will not exclude the diagnosis, as there are more, as-yet-undiscovered genes that cause NS. Thus, the diagnosis of NS 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. The principal values of making a genetic 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 hypertrophic cardiomyopathy in patients with a mutation of KRAS and an increased risk of juvenile myelomonocytic leukemia for a mutation of PTPN11. In the future, studies may lead to a targeted management of NS symptoms that depends on what genetic mutation a patient has.
Intra uterine ultrasound
First trimester ultrasound of noonan syndrome reveals nuchal oedema / cystic hygroma almost same as seen in Turner syndrome. Follow up scans may shows clinical features that already described above.
A 2007 study followed 112 individuals for a mean of 12 years (mean age 25.3, range 12–71). No patient died during follow-up, but several required medical interventions. The mean final heights were 167 and 153 cm for men and women, respectively, which is approximately 2 standard deviations below normal.
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. These characteristics were sometimes seen running in families but were not associated with gross chromosomal abnormalities. She studied 833 patients at the congenital heart disease clinic, looking for other congenital abnormalities, and in 1963 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 facial features, chest deformities and short stature.
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 produced a paper entitled "Hypertelorism with Turner Phenotype" in 1968, and in 1971 at the Symposium of Cardiovascular defects, the name 'Noonan syndrome' became officially recognized.
- Turner syndrome, a different disorder often confused with NS because of several physical features that they share
- Fetal alcohol syndrome, another disorder sometimes confused with NS because of some common facial features and intellectual disability
- Other RASopathies, particularly:
- Costello syndrome
- Legius syndrome
- Noonan Syndrome with Multiple Lentigines, as known as 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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- "Noonan syndrome" at Dorland's Medical Dictionary
- "Does Noonan Syndrome Increase Malignant Hyperthermia Susceptibility?". Malignant Hyperthermia Association of the United States. Retrieved 24 October 2014.
- "Imbalance of plasminogen activator inhibitor type-1 (PAI-1) and tissue plasminogen activator (t-PA) activity in patients with Noonan syndrome". J Pediatr Hematol Oncol. 32 (7): 532–6. Oct 2010. doi:10.1097/MPH.0b013e3181e0d152. PMID 20686427.
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