A 16-year-old boy has acral enlargement and coarse facial features. Serum growth hormone is markedly elevated, but serum IGF-1 is at the lower limit of normal. Which of the following best explains the discordance between the two hormone levels?
- A IGF-1 is synthesized primarily by the anterior pituitary under independent control
- B IGF-1 is rapidly degraded because of absent carrier proteins in this patient
- C Chronic protein-calorie malnutrition has reduced hepatic IGF-1 synthesis despite high GH ✓
- D IGF-1 secretion requires prolactin co-secretion from the same pituitary cells
Correct answer: C. Chronic protein-calorie malnutrition has reduced hepatic IGF-1 synthesis despite high GH
Explanation
Most circulating IGF-1 is produced by the liver in response to growth hormone, acting through the JAK2-STAT pathway. Hepatic IGF-1 generation is highly nutrition sensitive, so protein-energy malnutrition blunts IGF-1 output even when GH levels are high, producing resistance to GH action at the tissue level. Option A is wrong because the pituitary secretes GH, not IGF-1. Carrier proteins are abundant and not absent in malnutrition, eliminating B.
Reference: Harper's Illustrated Biochemistry, 31st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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