Contribution of functionally assessed GHRHR mutations to idiopathic isolated growth hormone deficiency in patients without GH1 mutations

Identification and functional analysis of first heterozygous frameshift mutation in the GHRH gene in a Chinese boy with isolated growth hormone deficiency

BACKGROUND

Isolated growth hormone deficiency (IGHD) is a rare genetically heterogeneous disorder caused primarily by mutations in GH1 and GH releasing hormone receptor (GHRHR). The aim of this study was to identify the molecular etiology of a Chinese boy with IGHD.

METHODS

Whole-exome sequencing, sanger sequencing and bioinformatic analysis were performed to screen for candidate mutations. The impacts of candidate mutation on gene expression, intracellular localization and protein function were further evaluated by in vitro assays.

RESULTS

A novel heterozygous frameshift mutation in the GHRH gene (c.91dupC, p.R31Pfs*98) was identified in a Chinese boy clinically diagnosed as having IGHD. The mutation was absent in multiple public databases, and considered as deleterious using in silico prediction, conservative analysis and three-dimensional homology modeling. Furthermore, mRNA and protein expression levels of mutant GHRH were significantly increased than wild-type GHRH (p < 0.05). Moreover, mutant GHRH showed an aberrant accumulation within the cytoplasm, and obviously reduced ability to stimulate GH secretion and cAMP accumulation in human GHRHR-expressing pituitary GH3 cells compared to wild-type GHRH (p < 0.05).

CONCLUSION

Our study discovered the first loss-of function mutation of GHRH in a Chinese boy with IGHD and provided new insights on IGHD pathogenesis caused by GHRH haploinsufficiency.

Genetic diagnosis of congenital hypopituitarism in Turkish patients by a target gene panel: novel pathogenic variants in GHRHR, GLI2, LHX4 and POU1F1 genes

Objective

Congenital hypopituitarism (CH) is a rare disease characterized by one or more hormone deficiencies of the pituitary gland. To date, many genes have been associated with CH. In this study, we identified the allelic variant spectrum of 11 causative genes in Turkish patients with CH.

Materials and methods

This study included 47 patients [21 girls (44.6%) and 26 boys (55.4%)] from 45 families. To identify the genetic etiology, we screened 11 candidate genes associated with CH using next-generation sequencing. To confirm and detect the status of the specific familial variant in relatives, Sanger sequencing was also performed.

Results

We identified 12 possible pathogenic variants in GHRHR, GH1, GLI2, PROP-1, POU1F1, and LHX4 in 11 patients (23.4%), of which six were novel variants: two in GHRHR, two in POU1F1, one in GLI2, and one in LHX4. In all patients, these variants were most frequently found in GLI2, followed by PROP-1 and GHRHR.

Conclusion

Genetic causes were determined in only 23.4% of all patients with CH and 63% of molecularly diagnosed patients (7/11) from consanguineous families. Despite advances in genetics, we were unable to identify the genetic etiology of most patients with CH, suggesting the effect of unknown genes or environmental factors. More genetic studies are necessary to understand the etiology of CH.

Characterization of Somatotrope Cell Expansion in Response to GHRH in the Neonatal Mouse Pituitary

In humans and mice, loss-of-function mutations in growth hormone-releasing hormone receptor (GHRHR) cause isolated GH deficiency. The mutant GHRHR mouse model, GhrhrLit/Lit (LIT), exhibits loss of serum GH, but also fewer somatotropes. However, how loss of GHRH signaling affects expansion of stem and progenitor cells giving rise to GH-producing cells is unknown. LIT mice and wild-type littermates were examined for differences in proliferation and gene expression of pituitary lineage markers by quantitative reverse transcription polymerase chain reaction and immunohistochemistry at postnatal day 5 (p5) and 5 weeks. At p5, the LIT mouse shows a global decrease in pituitary proliferation measured by proliferation marker Ki67 and phospho-histone H3. This proliferative defect is seen in a pituitary cell expressing POU1F1 with or without GH. SOX9-positive progenitors show no changes in proliferation in p5 LIT mice. Additionally, the other POU1F1 lineage cells are not decreased in number; rather, we observe an increase in lactotrope cell population as well as messenger RNA for Tshb and Prl. In the 5-week LIT pituitary, the proliferative deficit in POU1F1-expressing cells observed neonatally persists, while the number and proliferative proportion of SOX9 cells do not appear changed. Treatment of cultured pituitary explants with GHRH promotes proliferation of POU1F1-expressing cells, but not GH-positive cells, in a mitogen-activated protein kinase-dependent manner. These findings indicate that hypothalamic GHRH targets proliferation of a POU1F1-positive cell, targeted to the somatotrope lineage, to fine tune their numbers.

A GHRHR founder mutation causes isolated growth hormone deficiency type IV in a consanguineous Pakistani family

Background

Isolated growth hormone deficiency (IGHD) is caused by a severe shortage or absence of growth hormone (GH), which results in aberrant growth and development. Patients with IGHD type IV (IGHD4) have a short stature, reduced serum GH levels, and delayed bone age.

Objectives

To identify the causative mutation of IGHD in a consanguineous family comprising four affected patients with IGHD4 (MIM#618157) and explore its functional impact in silico.

Methods

Clinical and radiological studies were performed to determine the phenotypic spectrum and hormonal profile of the disease, while whole-exome sequencing (WES) and Sanger sequencing were performed to identify the disease-causing mutation. In-silico studies involved protein structural modeling and docking, and molecular dynamic simulation analyses using computational tools. Finally, data from the Qatar Genome Program (QGP) were screened for the presence of the founder variant in the Qatari population.

Results

All affected individuals presented with a short stature without gross skeletal anomalies and significantly reduced serum GH levels. Genetic mapping revealed a homozygous nonsense mutation [NM_000823:c.G214T:p.(Glu72*)] in the third exon of the growth-hormone-releasing hormone receptor gene GHRHR (MIM#139191) that was segregated in all patients. The substituted amber codon (UAG) seems to truncate the protein by deleting the C-terminus GPCR domain, thus markedly disturbing the GHRHR receptor and its interaction with the growth hormone-releasing hormone.

Conclusion

These data support that a p.Glu72* founder mutation in GHRHR perturbs growth hormone signaling and causes IGHD type IV. In-silico and biochemical analyses support the pathogenic effect of this nonsense mutation, while our comprehensive phenotype and hormonal profiling has established the genotype-phenotype correlation. Based on the current study, early detection of GHRHR may help in better therapeutic intervention.

Whole Exome Sequencing Uncovered the Genetic Architecture of Growth Hormone Deficiency Patients

PURPOSE

Congenital growth hormone deficiency (GHD) is a rare and etiologically heterogeneous disease. We aim to screen disease-causing mutations of GHD in a relatively sizable cohort and discover underlying mechanisms via a candidate gene-based mutational burden analysis.

METHODS

We retrospectively analyzed 109 short stature patients associated with hormone deficiency. All patients were classified into two groups: Group I (n=45) with definitive GHD and Group II (n=64) with possible GHD. We analyzed correlation consistency between clinical criteria and molecular findings by whole exome sequencing (WES) in two groups. The patients without a molecular diagnosis (n=90) were compared with 942 in-house controls for the mutational burden of rare mutations in 259 genes biologically related with the GH axis.

RESULTS

In 19 patients with molecular diagnosis, we found 5 possible GHD patients received known molecular diagnosis associated with GHD (NF1 [c.2329T>A, c.7131C>G], GHRHR [c.731G>A], STAT5B [c.1102delC], HRAS [c.187_207dup]). By mutational burden analysis of predicted deleterious variants in 90 patients without molecular diagnosis, we found that POLR3A (p = 0.005), SUFU (p = 0.006), LHX3 (p = 0.021) and CREB3L4 (p = 0.040) represented top genes enriched in GHD patients.

CONCLUSION

Our study revealed the discrepancies between the laboratory testing and molecular diagnosis of GHD. These differences should be considered when for an accurate diagnosis of GHD. We also identified four candidate genes that might be associated with GHD.

Structural basis for activation of the growth hormone-releasing hormone receptor

Growth hormone-releasing hormone (GHRH) regulates the secretion of growth hormone that virtually controls metabolism and growth of every tissue through its binding to the cognate receptor (GHRHR). Malfunction in GHRHR signaling is associated with abnormal growth, making GHRHR an attractive therapeutic target against dwarfism (e.g., isolated growth hormone deficiency, IGHD), gigantism, lipodystrophy and certain cancers. Here, we report the cryo-electron microscopy (cryo-EM) structure of the human GHRHR bound to its endogenous ligand and the stimulatory G protein at 2.6 Å. This high-resolution structure reveals a characteristic hormone recognition pattern of GHRH by GHRHR, where the α-helical GHRH forms an extensive and continuous network of interactions involving all the extracellular loops (ECLs), all the transmembrane (TM) helices except TM4, and the extracellular domain (ECD) of GHRHR, especially the N-terminus of GHRH that engages a broad set of specific interactions with the receptor. Mutagenesis and molecular dynamics (MD) simulations uncover detailed mechanisms by which IGHD-causing mutations lead to the impairment of GHRHR function. Our findings provide insights into the molecular basis of peptide recognition and receptor activation, thereby facilitating the development of structure-based drug discovery and precision medicine.

Growth hormone-releasing hormone (GHRH) controls metabolism and tissue growth through binding to the cognate receptor (GHRHR). Here authors report the structure of the human GHRHR bound to its endogenous ligand and the stimulatory G protein which reveals a characteristic hormone recognition pattern of GHRH by GHRHR.

Polymorphism of the growth hormone gene GH1 in Polish children and adolescents with short stature

PURPOSE

Short stature in children is a significant medical problem which, without proper diagnosis and treatment, can lead to long-term consequences for physical and psychological health in adult life. Since human height is a polygenic and highly heritable trait, numerous variants in the genes involved in growth-including the growth hormone (GH1) gene-have been identified as causes of short stature.

METHODS

In this study, we performed for the first time molecular analysis of the GH1 gene in a cohort (n = 186) of Polish children and adolescents with short stature, suffering from growth hormone deficiency (GHD) or idiopathic short stature (ISS), and a control cohort (n = 178).

RESULTS

Thirteen SNP variants were identified, including four missense variants, six in 5'UTR, and three in introns. The frequency of minor missense variants was low (<0.02) and similar in the compared cohorts. However, two of these variants, Ala39Val (rs151263636) and Arg42Leu (rs371953554), were found (heterozygote status) in only two GHD patients. These substitutions, according to databases, can potentially be deleterious.

CONCLUSIONS

Mutations of GH1 causing short stature are very rare in the Polish population, but two potentially causative variants need further studies in a larger cohort of GHD patients.