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.