A 4-year-old boy is evaluated for short stature. He has hypertelorism, downslanting palpebral fissures, low-set posteriorly rotated ears, short webbed neck, and pectus carinatum. Echocardiography shows valvular pulmonary stenosis with mild hypertrophic cardiomyopathy. His karyotype is 46,XY. What is the most likely diagnosis?
- A Noonan syndrome ✓
- B Turner syndrome
- C LEOPARD syndrome
- D Williams syndrome
Correct answer: A. Noonan syndrome
Explanation
Noonan syndrome phenocopies Turner syndrome in facial features, webbed neck, and short stature, but occurs in both sexes with a normal karyotype, classically involving PTPN11 mutation. The characteristic cardiac lesion is pulmonary valve stenosis with possible hypertrophic cardiomyopathy, whereas Turner syndrome typically produces a left-sided obstructive lesion such as coarctation or bicuspid aortic valve. The normal 46,XY karyotype excludes Turner syndrome.
Reference: Nelson Textbook of Pediatrics, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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