Noonan syndrome

Noonan syndrome (NS) is a genetically and phenotypically heterogenous non aneuploidic congenital RASopathy. Affected individuals can bear some clinical features similar to that of Turner syndrome

The estimated incidence is at ~1 in 1000-2500 11. As individuals have normal number of chromosomes, both males and females can be affected.  

An immense number of clinical features have been described which can be present at varying degrees. These include:

  • dilated renal pelves 7,10

The inheritance is autosomal dominant although a significant proportion of cases are sporadic 9. Many genes have been implicated, the most common being the PTPN11 gene which encodes for SHP2, which results in an inability to inactivate SHP2 causing increased signalling of the Ras/MAPK pathway. However. other genes that may be less commonly implicated including SOS1KRASRAF1NRAS, and SHOC2 11. Because of its effect in amplifying the Ras/MAPK pathway, it is considered to be a RASopathy 11.

Early 1st trimester ultrasound may show nuchal oedema or a cystic hygroma similar to that of Turner syndrome. With subsequent scanning, some of the above individual clinical features may be present sonographically.

It is named after Jacqueline Noonan (1928-), an American paediatric cardiologist 1.

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Article information

rID: 11103
Synonyms or Alternate Spellings:
  • Noonan's syndrome
  • Pseudo-Turner syndrome

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