Identification of a novel splicing mutation in the growth hormone (GH)-releasing hormone receptor gene in a Chinese family with pituitary dwarfism

Abstract

A Chinese family with autosomal recessive pituitary dwarfism was identified and the proband was evaluated by MRI and hormonal analysis, which revealed pituitary dwarfism with a complete growth hormone deficiency. MRI showed a pituitary gland with a small anterior pituitary of 2.2 mm and evidence of hypoplastic pituitary. Linkage analysis with markers spanning 17 known genes for dwarfism revealed linkage of the family to the growth hormone-releasing hormone receptor (GHRHR) gene. Mutational analysis of all exons and exon–intron boundaries of GHRHR was carried out using direct DNA sequence analysis. A novel homozygosis mutation, a G to A transition located in the splice donor site at the beginning of intron 8 (IVS8+1G>A), was identified in the proband. The two other patients in the family are homozygous, whereas the living mother of the proband is heterozygous for the IVS8+1G>A mutation. The mutation was not found in 100 normal chromosomes from healthy Chinese individuals of Han nationality. An in vitro splicing assay using HeLa cells transfected with expression vectors containing the normal or the mutant GHRHR minigenes consisting of genomic fragments spanning exons 7–9 showed that the IVS8+1G>A mutation caused abnormal splicing, which is predicted to give rise to truncation or frameshift, leading to severely truncated GHRHR proteins. These results provide strong evidence that the splicing mutation IVS8+1G>A of GHRHR is a cause of pituitary dwarfism in the Chinese family.