A homozygous point mutation in the GH1 promoter (c.-223C>T) leads to reduced GH1 expression in siblings with isolated GH deficiency (IGHD)

Abstract

Context: Mutations in the GH1 promoter are a rare cause of isolated growth hormone deficiency (IGHD). Objective: To identify the molecular aetiology of a family with IGHD. Design: DNA sequencing, electromobility shift (EMSA) and luciferase reporter assays. Setting: University Hospital. Patients: Three siblings (2M) born to consanguineous parents presented with IGHD with normal pituitary on MRI. Methods: The GH1 proximal promoter, locus control region, five exons and four introns as well as GHRHR gene were sequenced in genomic DNA by Sanger method. DNA-protein interaction was evaluated by EMSA in nuclear extracts of GH3 pituitary cells. Dual-luciferase reporter assays were performed in cells transiently transfected with plasmids containing four different combinations of GH1 allelic variants (AV). Results: The patients harboured two homozygous variants (c.-185T>C and c.-223C>T) in the GH1 promoter within a highly conserved region and predicted binding sites for POU1F1/SP1 and SP1 respectively. The parents and brother were carriers and these variants were absent in 100 controls. EMSA demonstrated absent binding of GH3 nuclear extract to the c.-223C>T variant and normal binding of both POU1F1 protein and GH3 nuclear extract to the c.-185T>C variant. In contrast to GH1 promoter with AV only at c.-185, the GH1 promoter containing the AV only at c.-223 and at both positions drove significantly less expression of luciferase compared with the promoter containing either positions wild type in luciferase reporter assays. Conclusion: To our knowledge, c.-223C>T is the first homozygous point mutation in the GH1 promoter that leads to short stature due to IGHD.