ESPE Abstracts

Background: Main features of the autosomal dominant form of GH deficiency (IGHD II) include markedly reduced secretion of GH combined with low concentrations of IGF-I leading to short stature.

Objective and hypotheses: We report on a girl referred for assessment of short stature (−4.6 SDS) at a chronological age of 7 yr 10 mo. The GH deficiency was confirmed by standard GH provocation tests, which revealed severely reduced GH and IGF-I concentrations. Genetic analysis of the GH-1 gene identified heterozygosity for p.Q181R mutation and therefore IGHD II was diagnosed.

Method: We aimed to characterize the new p.Q181R mutation by in vitro GH secretion study as well as in silico mutagenesis and molecular dynamics simulations. Moreover, we performed a detailed structural analysis concerning folding, stability and dimerization of the mutant by generating recombinant wt-GH and mutant GH protein in Escherichia coli.

Results: In line with the clinical data of the patient, AtT-20 cells coexpressing both the wt-GH and the p.Q181R showed a reduced GH secretion after forskolin stimulation compared with cells expressing only wt-GH. Moreover; In silico mutagenesis and molecular dynamics simulations revealed a drastic change in interatomic contacts between the N and C terminus helices in hGH while the structural analyses of the mutant demonstrated a difference in folding and stability compared to the wt-GH.

Conclusion: p.Q181R seems to severely impair the regulated GH secretion and may, therefore, cause this specific form of IGHD II. Our results suggest that the specific and detailed analysis of this mutant may shed light on a new mechanism of secretory pathophysiology causing IGHD II.