Noonan syndrome

Last reviewed: 25 Aug 2023
Last updated: 14 Oct 2021



History and exam

Key diagnostic factors

  • positive family history
  • short stature
  • dysmorphic facial features
  • cryptorchidism
  • cardiac anomalies
  • delayed puberty
  • easy bruising or bleeding
  • lymphedema
  • pigmentary anomalies
  • sparse or absent eyebrows and lashes
  • splenomegaly
More key diagnostic factors

Other diagnostic factors

  • abnormalities identified prenatally
  • chest deformity
  • developmental delay/learning difficulty
  • skeletal anomalies
  • muscle weakness
  • history of renal malformation
Other diagnostic factors

Risk factors

  • family history of NS
  • advanced paternal age
More risk factors

Diagnostic investigations

1st investigations to order

  • ECG
  • echocardiogram
More 1st investigations to order

Investigations to consider

  • CBC
  • coagulation profile
  • molecular genetic testing
  • abdominal ultrasound
  • renal ultrasound
More investigations to consider

Treatment algorithm


all patients



David A. Stevenson, MD

Associate Professor

Department of Pediatrics

Division of Medical Genetics

Stanford University




DAS has acted as a consultant for Lineagen, GLG, and Alexion, and has given expert testimony. He is on the medical advisory board for parents' support groups for Costello syndrome and CFC syndrome. DAS is an author of a reference cited in this topic. DAS has also been reimbursed by RASopathies Network for attending conferences.


Dr David A. Stevenson would like to gratefully acknowledge Dr Judith E. Allanson, the previous contributor to this topic. JEA is an author of a number of references cited in this topic.

Peer reviewers

Liliana N. Contreras, MD


Endocrine Research Department

Instituto de Investigaciones Médicas Alfredo Lanari


University of Buenos Aires



LNC declares that she has no competing interests.

Bruce Gelb, MD

Professor of Pediatrics

Mount Sinai School of Medicine

New York



BG received royalties from GeneDx, Correlegan, Preventative Genetics, Baylor College of Medicine, and Harvard Medical School/Partners for genetic testing of Noonan syndrome. BG is an author of a number of references cited in this topic.

Jacqueline Noonan, MD

Professor Emeriti

Department of Pediatrics

College of Medicine

University of Kentucky




JN is on the Noonan Syndrome Advisory Board for Novo Nordisk and has received payment for speaking at a symposium. JN is an author of a number of references cited in this topic.

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