Question 1

Q: A 3-year-old girl is referred for evaluation of short stature and developmental concerns. On examination, she has a broad chest with widely spaced nipples, low posterior hairline, bilateral ptosis, low-set ears, and mild pulmonic stenosis on echocardiogram. Her chromosomal analysis reveals a 46,XX karyotype. Which of the following additional findings would most strongly support the unifying diagnosis in this child compared with the most phenotypically similar condition in the differential?

Hypertrophic cardiomyopathy and PTPN11 gene mutation. ***Hypertrophic cardiomyopathy and PTPN11 gene mutation*** - The presentation of **Noonan syndrome** features a **46,XX karyotype** and **pulmonic stenosis**, which distinguishes it from the phenotypically similar **Turner syndrome**. - A mutation in the **PTPN11 gene** and findings of **hypertrophic cardiomyopathy** are highly specific for Noonan syndrome and support the unifying diagnosis. *Webbed neck and short fourth metacarpal* - These features are seen in both **Noonan syndrome** and **Turner syndrome**, making them poor discriminators between the two conditions. - While common in dwarfism/skeletal dysplasias, they do not help isolate the **46,XX** Noonan phenotype from the **45,X** Turner phenotype. *Bicuspid aortic valve and 45,X karyotype* - This clinical picture describes **Turner syndrome**, but the patient in the vignette has a normal **46,XX karyotype**. - **Bicuspid aortic valve** is a classic left-sided heart defect associated with Turner syndrome, whereas Noonan syndrome typically involves **right-sided defects**. *Coarctation of the aorta and 45,X karyotype* - These findings are pathognomonic for **Turner syndrome** and contradict the patient's documented **46,XX karyotype**. - Pulmonary stenosis is rarely seen in Turner syndrome, while **coarctation of the aorta** is a hallmark finding absent in Noonan syndrome. *Ventricular septal defect and 47,XX+21 karyotype* - This karyotype identifies **Down syndrome** (Trisomy 21), which presents with distinct facial features like **epicanthal folds** and **upslanting palpebral fissures**. - While **ventricular septal defects** are common in Down syndrome, they do not align with the patient’s observed **ptosis** or **pulmonic stenosis**.

Question

A 3-year-old girl is referred for evaluation of short stature and developmental concerns. On examination, she has a broad chest with widely spaced nipples, low posterior hairline, bilateral ptosis, low-set ears, and mild pulmonic stenosis on echocardiogram. Her chromosomal analysis reveals a 46,XX karyotype. Which of the following additional findings would most strongly support the unifying diagnosis in this child compared with the most phenotypically similar condition in the differential?

Accepted Answer

Hypertrophic cardiomyopathy and PTPN11 gene mutation

Answer

Webbed neck and short fourth metacarpal

Answer

Bicuspid aortic valve and 45,X karyotype

Answer

Coarctation of the aorta and 45,X karyotype

Answer

Ventricular septal defect and 47,XX+21 karyotype

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