Short stature in two siblings heterozygous for a novel bioinactive GH mutant (GH-P59S) suggesting that the mutant also affects secretion of the wild-type GH

Abstract

Objective: Short stature caused by biologically inactive GH is clinically characterized by lack of GH action despite normal-high secretion of GH, pathologically low IGF1 concentrations and marked catch-up growth on GH replacement therapy. Design and methods: Adopted siblings (girl and a boy) of unknown family history were referred for assessment of short stature (K4.5 and K5.6 SDS) at the age of 10 and 8.1 years respectively. They had delayed bone ages (6.8 and 4.5 years), normal GH peaks at stimulation tests, and severely reduced IGF1 concentrations (K3.5 and K4.0 SDS). Genetic analysis of the GH1 gene showed a heterozygous P59S mutation at position involved in binding to GH receptor (GHR). Results: Isoelectric focusing analysis of secreted GH in patient serum revealed the presence of higher GH-P59S peak compared with that of wt-GH. Furthermore, computational simulation of GH-P59S binding to GHR suggested problems in correct binding of the mutant to the GHR. In vitro GHR binding studies revealed reduced binding affinity of GH-P59S for GHR (IC50, 30 ng/ml) when compared with the wt-GH (IC50, 11.8 ng/ml) while a significantly decreased ability of the mutant to activate the Jak2/Stat5 signaling pathway was observed at physiological concentrations of 25-100 ng/ml. Conclusions: The clinical and biochemical data of our patients support the diagnosis of partial bioinactive GH syndrome. The higher amount of GH-P59S secreted in their circulation combined with its impact on the wt-GH function on GHR binding and signaling may alter GHR responsiveness to wt-GH and could ultimately explain severe short stature found in our patients. © 2013 European Society of Endocrinology.