USMLE PRACTICE QUESTION OF THE WEEK

Question for August 29, 2025

A 16-year-old girl is evaluated for primary amenorrhea. She has normal breast development but scant pubic and axillary hair. Pelvic ultrasound shows an absent uterus and blind-ending vaginal pouch. Karyotype reveals 46,XY.

Which of the following is the most likely cause of her presentation?

A. Aromatase deficiency

B. Complete androgen insensitivity syndrome

C. Kallmann syndrome

D. Mayer-Rokitansky-Küster-Hauser syndrome

E. Turner syndrome

Get Detailed Explanation

Correct Answer:

B. Complete androgen insensitivity syndrome

Step-by-Step Explanation:

Step 1: 46,XY karyotype with female external genitalia and absent uterus suggests a disorder of sexual development.

Step 2: Normal breast development (due to peripheral conversion of androgens to estrogens) but absent pubic/axillary hair point toward complete androgen insensitivity syndrome (CAIS), where tissues are unresponsive to androgens.

Step 3: Testes are present but undescended or intra-abdominal.

Why These Are Incorrect:

A. Aromatase deficiency would cause virilization, not typical female appearance.
C. Kallmann syndrome causes hypogonadotropic hypogonadism and absent puberty.
D. MRKH syndrome presents with 46,XX karyotype and normal secondary sexual characteristics.
E. Turner syndrome is 45,XO and features short stature, not normal breast development.