Familial isolated growth hormone deficiency due to a novel homozygous missense mutation in the growth hormone releasing hormone receptor gene: Clinical presentation with hypoglycemia

Abstract

Context: Mutations in the growth hormone releasing hormone receptor (GHRHR) gene are a relatively rare cause of isolated growth hormone deficiency (IGHD). Objective: This study aimed to understand the biochemical basis of hypoglycemia in the index case and the molecular basis of severe short stature in a large consanguineous family with IGHD. Patients and Methods: The index case presented with a hypoglycemic convulsion, following which eight members in two related consanguineous Turkish families were identified with IGHD. Homozygosity mapping identified the homozygous regions shared only among the affected individuals. Sanger sequencing of GHRHR, which resided in the shared homozygous region, was performed. In silico analysis of the pathogenic GHRHR variant was performed. Results: The clinical presentation and hormonal analysis confirmed GH deficiency in all affected individuals. Magnetic resonance imaging scan of the pituitary gland showed anterior pituitary hypoplasia in five affected individuals in which the youngest was only 0.4 years old, but with normal pituitary size in three affected individuals. Homozygosity mapping showed two large homozygous regions on chromosome 7 shared only among affected individuals. Sanger sequencing of GHRHR gene present in one of these shared regions identified a novel homozygous missense mutation (p.C64G) segregating with the disease phenotype. In silico analysis predicted the mutation to be deleterious and disease causing. Conclusions: We describe a large consanguineous Turkish kindred with IGHD due to a novel homozygous missense GHRHR mutation. This is the first description of presentation with hypoglycemia and the earliest reported occurrence of anterior pituitary hypoplasia in patients with GHRHR mutation.