Noonan syndrome

Illustration of Noonan syndrome

Syndrome description

Noonan syndrome is a dysmorphic syndrome characterized after birth by: a particular aspect of facial features (hypertelorism, a downward eye slant, low-set posteriorly rotated ears), short stature, a webbed neck, cardiac anomalies, deafness, motor delay, and a bleeding diathesis. Sometimes there is an intellectual deficit and a delay in language acquisition.
The final diagnosis of Noonan syndrome is also challenging in postnatal life, and it is based on clinical features due to its genetic heterogenety; several scoring systems have been used.


4 children out of 10.000

Noonan syndrome affects boys and girls equally. This disease is not specific to a particular population or region.


Orpha: 648
OMIM: 163950  605275  609942  610733  611553  613224  613706  615355  616559  616564  618499  618624  619087
UMLS: C0028326
MeSH: D009634
GARD: 10955
MedDRA: 10029748

A bit of history

The first complete description appears to be that of Weissenberg in 1928.
In 1963, Jacqueline Noonan, cardiopediatrician further delineated the clinical phenotype and documented its association with valvular pulmonic stenosis.

Anomalies detectable by ultrasound

Anomalies: very frequent – 80% or more

1st trimester

  • Cystic hygroma
  • Increased nuchal translucency

2nd and 3rd trimester

  • Thickened nuchal skin fold
  • Webbed neck
  • High forehead
  • Downslanted palpebral fissures
  • Low-set, posteriorly rotated ears
  • Hypertelorism
  • Thickened helices
  • Excessive amount of amniotic fluid

3D assessment of the fetal face may sometimes show the typical coarse facies described postnatally.

Anomalies: frequent 30 – 80%

1st trimester

  • Polyhydramnios
  • Hypertelorism
  • Abnormality of the eye

2nd and 3rd trimester

  • Pleural effusion
  • Ascites
  • Cryptorchidism
  • Hypoplasia of nasal bones
  • Short femur
  • Hypertrophic cardiomyopathy
  • Peripheral pulmonary stenosis
  • Pulmonary valve stenosis
  • Abnormal ductus venosus doppler (reversed a-wave)

Anomalies : occasional < 30%

1st trimester

  • Abnormality of the umbilical cord
  • Abnormal heart morphology
  • Ventricular septal defect
  • Atrial septal defect
  • Increased nuchal translucency (T1)
  • External ear malformation
  • Pleural effusion

2nd and 3rd trimester

  • Hydrops
  • Aplasia of the semicircular canal
  • Edema of the dorsum of the hands and feet
  • Absence of Ductus Venosus
  • Persistence of the Right Umbilical Vein Hydrothorax
  • Chylothorax
  • Atrial septal defect
  • Ventricular septal defect
  • Tetralogy of Fallot
  • Aortic coarctation
  • Aortic stenosis
  • Atrioventricular canal

Differential diagnosis

Differential diagnoses include Cardio-Facio-Cutaneous syndrome, Costello syndrome, Neurofibromatosis type 1, Noonan syndrome with multiple lentigines (all RASopathies), Baraitser-Winter, Aarskog and Escobar syndromes.

Expert editor: Emmanuel Spaggiari – Last update: 15 May 2022

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Emmanuel Spaggiari
Emmanuel Spaggiari
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