NOONAN SYNDROME

Noonan syndrome is characterized by dysmorphic facial features, webbed neck, short stature, cardiac and lymphatic abnormalities and varying degrees of mental retardation. The diagnosis is often not made in utero or in early childhood, and is only confirmed during the late childhood years.

Incidence: 1/1-2000.
Inheritance: Autosomal Dominant or Sporadic. Gene responsible for the defect has been located on the short arm of chromosme 12 (3).

Phenotypically similar to Turner’s syndrome, however the karyotype is normal.

ULTRASOUND

1. Increased nuchal translucency / Nuchal edema (first or second trimester).
2. Short femur.
3. Cardiac anomaly:
1. Pulmonary valve anomalies (dysplastic or stenotic).
2. Hypertrophic cardiomyopathy.
3. Coarctation of the aorta.
4. VSD, PDA less frequently.
4. Fetal hydrops.
5. Pleural effusion.
6. Hypertelorism.
7. Low set ears.
8. Polyhydramnios (common) (4).
9. Single umbilical artery.
10. Persistent right umbilical vein.
11. Renal pyelectasis.

REFERENCES

1. Bradley E, Kean L, Twining P, James D. Persistent right umbilical vein in a fetus with Noonan’s syndrome: a case report. Ultrasound Obstet Gynecol 2001;17:76-78.

2. Leonidas JC, Fellows RA. Congenital absence of the ductus venosus with direct connection between the umbilical vein and the distal inferior vena cava. Radiology 1976;126:892-895.

3. Brady AF, van der Bergt I Crosby A et.al. Further delineation of the critical region for Noonan syndrome on the long arm of chromosome 12. Eur J Hum Genet 1997;5:336-337.

4. Menashe M, Arbel R, Raveh D et.al. Poor prenatal detection rate of cardiac anomalies in Noonan syndrome. Ultrasound Obstet Gynecol 2002;19:51-55.