A 9-year-old boy has severe short stature. Basal growth hormone is markedly elevated, serum IGF-1 is very low, and growth hormone receptors show impaired signaling on testing. Administration of recombinant growth hormone produces no growth acceleration. What is the diagnosis?

• A Growth hormone deficiency due to GHRH receptor mutation
• B IGF-1 excess from a hepatic tumor
• C Laron syndrome due to growth hormone receptor defect ✓
• D Hypothyroidism causing secondary growth failure

Explanation

Laron syndrome results from mutations in the growth hormone receptor or its downstream signaling, so GH cannot generate hepatic IGF-1. Loss of IGF-1 negative feedback leaves GH levels high, the inverse of true GH deficiency where both GH and IGF-1 are low. Because the defect lies distal to the receptor, exogenous GH is ineffective, whereas recombinant IGF-1 works, which distinguishes it from option A.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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