Noonan syndrome is a rare genetic disorder characterized by facial dysmorphism, short stature, heart defects, bleeding problems as well as skeletal malformations.
Noonan syndrome occurs in 1:1000 to 1:2500 people.
Noonan syndrome is an autosomal dominant disorder, as having only one copy of the altered or mutated gene is sufficient to cause the condition.
It is caused by a mutation in the PTPN11 gene and rarely in the SOS1, RAF1 and RIT1 gene.
These genes are involved in cell division and growth of cells as well in activation pathways in intracellular signal transduction involved in the differentiation of cells particularly in the semilunar heart valves e.g pulmonary valve, leading to pulmonary valve stenosis, a very classic complication of this disease.
Noonan syndrome is characterized by mild facial dysmorphism, including ocular hypertelorism (widely set eyes), ptosis and a micrognathia (small jaw). Other musculoskeletal deformities can occur such as a short webbed neck with trident hairline, pectus excavatum (sunken chest) and short stature.
Most people with Noonan syndrome have severe congenital heart defects, including hypertrophic cardiomyopathy, in which the myocardium (the muscle of the heart) is enlarged and weakened. Another typical defect is pulmonary valve stenosis, a narrowing of the pulmonary valve in the heart.
2/3 of people with Noonan syndrome, have a normal intelligence, however, occasionally mild learning difficulties can occur that are associated with vision and hearing problems.
Bleeding disorders can occur in around 20-30% of individuals with Noonan syndrome due to defects in the coagulation factors as well as due to low levels of platelets in the blood, which are crucial to ensure an adequate hemostasis (process responsible to stop bleeding).
Skin discoloration including light brown patches (café-au lait spots) and freckle-like spots on the skin are typical of this syndrome.
Noonan syndrome has very typical clinical manifestations, such as facial dysmorphism, skeletal abnormalities and heart defects, manifesting already during infancy which can lead to the suspicion of this disease at a young age.
Genetic testing of the involved genes confirms the diagnosis.
Antenatal diagnosis can be indicated by the presence of a cystic hygroma (swelling in the neck region) and increased nuchal translucency during a prenatal ultrasound.
The management of Noonan syndrome is focused on alleviating the symptoms and treating the complications.This includes possible heart surgery and growth hormone therapy to increase the height of the child. More recently, somatotropin injections can be used as a replacement of growth hormone therapy.
Special programs can be offered to children with learning disabilities.
The prognosis of Noonan syndrome depends on the severity of symptoms, particularly on the severity of the congenital heart defects.
Studies indicate that Noonan syndrome can increase the mortality rate by 3-fold compared with the general population, however most people can have a normal lifespan.
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