A newborn has a webbed neck, widely spaced nipples, peripheral edema of the hands and feet, low posterior hairline, coarctation of the aorta, and horseshoe kidney on ultrasound. Karyotype is 45,X. Which feature is MOST specific to this condition compared to Noonan syndrome?
- A Webbed neck and low posterior hairline
- B Pulmonary stenosis
- C 45,X karyotype and lymphedema at birth ✓
- D Short stature and coarctation of aorta
Explanation
This presentation is Turner syndrome (45,X monosomy). While Turner and Noonan syndromes share features like webbed neck, short stature, and cardiac defects, Turner syndrome is specifically characterized by 45,X (or 45,X mosaicism) karyotype, neonatal lymphedema (peripheral edema from lymphatic hypoplasia), and left-sided cardiac defects (coarctation of aorta, bicuspid aortic valve), whereas Noonan syndrome has normal karyotype (46,XX or 46,XY), right-sided defects (pulmonary stenosis, hypertrophic cardiomyopathy), and RAS pathway gene mutations (PTPN11 most commonly). Horseshoe kidney and gonadal dysgenesis are specific to Turner syndrome.
Reference: Ghai Essential Pediatrics, 10th ed.
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Written and medically reviewed by the StethoPrep medical team.