Near-normal linear growth in the setting of markedly reduced growth hormone and IGF-1 - A case report

A 14.2-year-old prepubertal boy diagnosed with complete-type growth hormone deficiency and tertiary hypothyroidism, keeps growing in the height range between -1 and -2 SD. He has been treated with levothyroxine only. To under stand the growth mechanism of this boy, we analyzed the serum growth hormon e (GH) with a radioimmunoassay (RIA), serum GH bioactivity with Nb2 and ery throid progenitor cell bioassays, and growth hormone-binding protein (GHBP) with a ligand-mediated immunofunctional assay (LIFA). In addition, IGF-1 a nd free IGF-1 were analyzed by immunoradiometric assay (IRMA) and insulin-l ike growth factor-binding protein3 (IGFBP-3) by Western immunoblot. Peak GH -RIA responses to insulin, arginine and GH-releasing factor, and nocturnal GH secretion, were low (0.5-2.3 ng/ml); bioactive GH was low (0.313 ng/ml), and GHBP was elevated (84 ng/ml). The serum levels of IGF-1 a nd free IGF- 1 were continuously low, 17.1-39.3 and 0.17-0.26 ng/ml, respectively. Moreo ver, serum IGFBP-3 levels were low (1.68-1.39 mg/l) and IGFBP-3 protease ac tivity was negative. Prolactin and insulin were in the normal range. The re sult of the assay for growth-promoting activity showed that the patient's s erum stimulated normal erythroid progenitor cells twice as potently as did healthy thin adult control serum. These results suggest that GH and IGF-1 a re not indispensable for maintaining physical growth in this boy. Thus, it appears that circulating GH and IGF-1 are not mandatory requirements for ma intaining normal physical growth, and other, as yet uncharacterized, pathwa ys or growth factors might be sufficiently compensatory under certain condi tions.