A 15-year-old boy has absent puberty with testicular volume 2 mL and no pubic hair. He reports he has never been able to smell odours since childhood. LH is 0.8 IU/L, FSH is 1.2 IU/L, and testosterone is 40 ng/dL. MRI shows absent olfactory bulbs. What is the diagnosis?

• A Kallmann syndrome ✓
• B Constitutional delay of growth and puberty
• C Isolated hypogonadotropic hypogonadism
• D Prader-Willi syndrome

Explanation

Kallmann syndrome is hypogonadotropic hypogonadism combined with anosmia, caused by failure of migration of GnRH neurons from the olfactory placode to the hypothalamus. Mutations in ANOS1 (KAL1), FGFR1, and other genes underlie it. Low LH and FSH exclude hypergonadotropic causes, and anosmia distinguishes it from isolated GnRH deficiency, where smell is intact. Constitutional delay would show a delayed bone age with eventual spontaneous puberty and normal olfaction.

Reference: Williams Textbook of Endocrinology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.