Question:

A 15-year-old girl is brought to the office for evaluation of primary amenorrhea. The patient's mother and older sisters underwent menarche around age 13. The patient has had no changes in weight or nipple discharge but has difficulty identifying various odors. She has no known medical conditions and has had no surgery. The patient takes no daily medications and does not use tobacco, alcohol, or illicit drugs. She is not sexually active. Height is at the 3rd percentile for age, with 4.8 cm (1.9 in) of growth noted in the last year. Visual fields are intact. No breast tissue is present, and there is no axillary or pubic hair. Ultrasound confirms the presence of a uterus and 2 normal-appearing ovaries. Serum FSH level is 2 mU/mL (normal: 4-30 mU/mL) and LH is 3 mU/mL (normal: 5-25 mU/mL). Karyotype analysis of this patient is most likely to show which of the following?

• A. 45,XO

• B. 46,XX

• C. 46,XY

• D. 47,XXX

• E. 47,XXY

  

Answer:
B. 46,XX

• Female karyotype with intact uterus & ovaries, consistent with Kallmann syndrome

🧠 Hypothalamic Development Issue (Congenital) 

⬇️
Kallmann Syndrome (GnRH-producing neurons fail to migrate to hypothalamus)

⬇️
🧠 GnRH Deficiency
⬇️
↓ GnRH Secretion →
↓ Stimulation of Anterior Pituitary
⬇️
↓ FSH & ↓ LH Secretion
⬇️
Impaired Gonadal Function (Hypogonadotropic Hypogonadism)
⬇️
No Ovarian Estrogen Production → Lack of Pubertal Development

⬇️

• No breast tissue

• No axillary/pubic hair

  
  ⬇️
  🧠 Anosmia (Lack of Smell)

  Due to GnRH neuron migration defect, affecting olfactory bulb development
  ⬇️
  🧠 Karyotype Result: 46,XX

  

  Image Source: JCI

Explanation of Other Options

45,XO (Turner Syndrome)

• Incorrect because Turner syndrome has streak ovaries, high FSH/LH due to ovarian failure, and typical short stature with webbed neck.

46,XY (Androgen Insensitivity Syndrome)

• Incorrect due to lack of uterus/ovaries; external female genitalia with internal testes.

47,XXX and 47,XXY (Extra Chromosomes)

• Incorrect as these syndromes do not fit the hypogonadotropic hypogonadism, anosmia, and pubertal delay seen in Kallmann syndrome.

Flashcards

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