A 15-year-old boy has not started pubertal development. He has anosmia, bilateral undescended testes, and normal karyotype (46,XY). FSH and LH are low. GnRH stimulation shows a blunted response. What is the diagnosis?

• A Constitutional delay of puberty
• B Kallmann syndrome ✓
• C Klinefelter syndrome
• D Primary hypogonadism

Explanation

Kallmann syndrome is a form of hypogonadotropic hypogonadism caused by defective migration of GnRH neurons from the olfactory placode to the hypothalamus, resulting in absent/impaired GnRH secretion. The hallmark is absent or impaired sense of smell (anosmia/hyposmia) combined with delayed/absent puberty, low FSH/LH, and blunted GnRH stimulation test. X-linked form involves KAL1 (anosmin-1) gene; autosomal forms involve FGFR1, PROKR2, etc. Constitutional delay has normal olfaction and delayed bone age. Klinefelter is 47,XXY with elevated FSH/LH. Primary hypogonadism shows elevated gonadotropins.

Reference: Ghai Essential Pediatrics, 10th ed.

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