Expression of serum insulin-like growth factors, insulin-like growth factor-binding proteins, and the growth hormone-binding protein in heterozygote relatives of Ecuadorian growth hormone receptor deficient patients

Paul J. Fielder, Jaime Guevara-Aguirret, Arlan L. Rosenbloom, Lena Carlsson, Raymond L. Hintz, Ron G. Rosenfeld

Research output: Contribution to journalArticle

40 Scopus citations

Abstract

Recently, an isolated population of apparent GH-receptor deficient (GHRD) patients has been identified in the Loja province of southern Ecuador. These individuals presented many of the physical and biochemical phenotypes characteristic of Laron-Syndrome and are believed to have a defect in the GH-receptor gene. In this study, we have compared the biochemical phenotypes between the affected individuals and their parents, considered to be obligate heterozygotes for the disorder. Serum GH, insulin-like growth factor I and II (IGF-I and IGF-II) levels were measured by RIA Insulin-like growth factor binding proteins. (IGFBPs) were measured by Western ligand blotting (WLB) of serum samples, following separation by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and relative quantitation of serum IGFBPs was performed with a scanning laser densitometer. Serum GH-binding protein (GHBP) levels were measured with a ligand-mediated immunofunctional assay using a monoclonal antibody raised against the GHBP. These values were then compared to values obtained from normal, sex-matched adult Ecuadorian controls, to determine if the above parameters were abnormal in the heterozygotes. The serum IGF-I levels of the GHRD patients were < 13% of control values for adults and 2% for children. However, the IGF-I levels of both the mothers and fathers were not significantly different from that of the control population. The serum IGF-II levels of the GHRD patients were approximately 20% of control values for adults and 12% for the children. The IGF-II levels of the mothers were reduced, but were not significantly different from that of the control population. However, IGF-II levels of the fathers were significantly lower than those of controls (64% of control male levels). WLB analysis of serum IGFBP levels of the affected subjects demonstrated increased IGFBP-2 and decreased IGFBP-3, suggesting an inverse relationship between these IGFBPs. The GHRD patients who had the lowest serum IGFBP-3 levels (as measured by WLB) demonstrated a serum protease activity that could proteolyze 125I-IGFBP-3. GHRD patients who had higher serum IGFBP-3 levels lacked this serum protease activity. There were no differences in the serum IGFBP profiles of the mothers or the fathers for either IGFBP-2 or IGFBP-3, and serum from both groups lacked the ability to significantly proteolyze 125I-IGFBP-3. While GHRD patients had very low levels of serum GHBP, some patients did have measurable GHBP levels. The mean GHBP levels of the mothers (76% of controls females) and father of control males), while reduced, did not significantly differ from those of controls. Thus, while serum IGF-II and GHBP levels were somewhat reduced in the parents of the GHRD patients, they do not appear to provide a reliable biochemical marker for heterozygosity of the defective gene.

Original languageEnglish (US)
Pages (from-to)743-750
Number of pages8
JournalJournal of Clinical Endocrinology and Metabolism
Volume74
Issue number4
DOIs
StatePublished - Apr 1992

ASJC Scopus subject areas

  • Endocrinology, Diabetes and Metabolism
  • Biochemistry
  • Endocrinology
  • Clinical Biochemistry
  • Biochemistry, medical

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