[GHBP, IGF-1 and IGFBP-3 serum levels in familial short-statured and normal-statured children]. / Concentración sérica de GHBP, IGF-1 e IGFBP-3 en niños con talla baja familiar y con talla normal.

BACKGROUND AND OBJECTIVE: Growth hormone binding protein (GHBP), insuline-like growth factor 1 (IGF-1) and insuline-like growth factor binding protein 3 (IGFBP-3) serum concentrations were studied in familial short-statured patients (FSS) and age-matched normal-statured subjects. The aim of the study was to ascertain whether differences in growth factors concentrations between groups could be shown and whether they may contribute to explaining the different patterns of growth in both groups. SUBJECTS AND METHOD: Serum samples of 38 FSS patients (20 boys) and 31 normal-statured subjects (15 boys) in Tanner I stage (prepubertal), were analysed in a central laboratory. All auxological parameters (height, growth velocity, target height, body mass index (BMI) and biochemical parameters (IGF-1 and IGFBP-3) were standardised for age and sex-matched subjects. GHBP values were expressed as percentage of specific binding. RESULTS: The studied populations were similar and no statistically-significant differences in chronological age, bone age and BMI were found. Height, growth velocity and target height were significantly lower in FSS patients compared with normal subjects (p < 0.0001). IGF-1, IGFBP-3 and GHBP concentrations were significantly lower in the FSS group (p < 0.01). Correlations were found between IGF-1 and IGFBP-3 (r = 0.56; p = 0.0004) and between IGF-1 and GHBP (r = 0.34; p = 0.03) in the FSS group. However, in the normal-statured group only BMI and GHBP were correlated (r = 0.5; p = 0.02). CONCLUSIONS: These results strongly support the importance of the GH/IGF-1 functional axis in the pattern of growth and probably contribute to understanding of the pathophysiologic basis of the auxological differences found between groups.

A novel dysfunctional growth hormone variant (Ile179Met) exhibits a decreased ability to activate the extracellular signal-regulated kinase pathway.

The pituitary-expressed GH1 gene was screened for mutation in a group of 74 children with familial short stature. Two novel mutations were identified: an Ile179Met substitution and a -360A-->G promoter variant. The Ile179Met variant was shown to exhibit a similar degree of resistance to proteolysis as wild-type GH, indicating that the introduction of Met does not cause significant misfolding. Secretion of Ile179Met GH from rat pituitary cells was also similar to that of wild type. Although receptor binding studies failed to show any difference in binding characteristics, molecular modeling studies suggested that the Ile179Met substitution might nevertheless perturb interactions between GH and the GH receptor loop containing the hotspot residue Trp169, thereby affecting signal transduction. The ability of the Ile179Met variant to activate a signal transducer and activator of transcription (STAT) 5-responsive luciferase reporter gene and induce phosphorylation of STAT 5 and ERK was therefore studied. In contrast to its ability to activate STAT 5 normally, activation of ERK by the Ile179Met variant was reduced to half that observed with wild type. Although differential effects on the activation of distinct signaling pathways by a mutant receptor agonist are unprecedented, these findings also suggest that the ERK pathway could play a role in mediating the action of GH.