A 19-year-old man presents with delayed puberty, micropenis, absent sense of smell since childhood, and low serum LH, FSH and testosterone. MRI shows aplasia of the olfactory bulbs. The underlying developmental defect is:
- A Failure of canalisation of the Rathke pouch remnant
- B Aplasia of the parvocellular neurons of the paraventricular nucleus
- C Failure of migration of GnRH neurons from the olfactory placode to the hypothalamus ✓
- D Absence of kisspeptin receptors on gonadotrophs
Correct answer: C. Failure of migration of GnRH neurons from the olfactory placode to the hypothalamus
Explanation
Kallmann syndrome results from failed embryonic migration of GnRH-secreting neurons, which originate in the medial olfactory placode and travel along olfactory axons to reach the arcuate and preoptic hypothalamus. Anosmia from olfactory bulb agenesis accompanies hypogonadotropic hypogonadism because both structures share this migratory pathway. Kisspeptin receptor defects cause normosmic hypogonadotropic hypogonadism, which kills option D as the distractor.
Reference: Williams Textbook of Endocrinology, 14th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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