Identification of novel GHRHR and GH1 mutations in patients with isolated growth hormone deficiency

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.

Phenotype-Genotype Correlations of GH1 Gene Variants in Patients with Isolated Growth Hormone Deficiency or Multiple Pituitary Hormone Deficiency

INTRODUCTION

Genetic forms of growth hormone deficiency (GHD) may occur as isolated GHD (IGHD) or as a component of multiple pituitary hormone deficiency (MPHD). This study aimed to present the clinical and molecular characteristics of patients with IGHD/MPHD due to the GH1 gene variants.

METHODS

A gene panel accommodating 25 genes associated with MPHD and short stature was used to search for small sequence variants. Multiplex ligation-dependent probe amplification was performed in patients with normal panel results to investigate gross deletion/duplications. Segregation in the family was performed by Sanger sequencing.

RESULTS

The GH1 gene variants were detected in 5 patients from four unrelated families. One patient had IGHD IA due to homozygous whole GH1 gene deletion and one had IGHD IB due to novel homozygous c.162C>G/p.(Tyr54*) variant. Two patients from a family had previously reported heterozygous c.291+1G>A/p.(?) variant in which clinical and genetic characteristics were compatible with IGHD II accompanying MPHD. One patient had clinical and laboratory characteristics of IGHD II with MPHD but the heterozygous c.468 C>T/p.(R160W) variant had conflicting results about the relationship with the phenotype.

CONCLUSION

Expanding our knowledge of the spectrum of GH1 gene variants by apprehending clinical and molecular data of more cases, helps to identify the genotype-phenotype correlation of IGHD/MPHD and the GH1 gene variants. These patients must be regularly followed up for the occurrence of additional pituitary hormone deficiencies.

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.

Genetic spectrum and predictors of mutations in four known genes in Asian Indian patients with growth hormone deficiency and orthotopic posterior pituitary: an emphasis on regional genetic diversity

CONTEXT

Regional variation in prevalence of genetic mutations in growth hormone deficiency (GHD) is known.

AIM

Study phenotype and prevalence of mutations in GH1, GHRHR, POU1F1, PROP1 genes in GHD cohort.

METHODS

One hundred and two patients {Isolated GHD (IGHD): 79; combined pituitary hormone deficiency (CPHD): 23} with orthotopic posterior pituitary were included. Auxologic, hormonal and radiological details were studied. All four genes were analysed in IGHD patients. POU1F1 and PROP1 were studied in CPHD patients.

RESULTS

Of 102, 19.6% were familial cases. Height SDS, mean (SD) was - 5.14 (1.63). Peak GH, median (range) was 0.47 ng/ml (0-6.59), 72.5% patients had anterior pituitary hypoplasia (APH). Twenty mutations (novel: 11) were found in 43.1% patients (n = 44, IGHD-36, CPHD-8). GHRHR mutations (n = 32, p.Glu72* = 24) were more common than GH1 mutations (n = 4) in IGHD cohort. POU1F1 mutations (n = 6) were more common than PROP1 mutations (n = 2) in CPHD cohort. With few exceptions, this prevalence pattern is contrary to most studies in world-literature. No patients with peak GH > 4 ng/ml had mutations, signifying it as negative predictor. While many parameters were significant on univariate analysis, only positive family history and lower median peak GH levels were significant predictors of mutations on multivariate analysis in IGHD patients.

CONCLUSION

At variance with world literature, we found reverse predominance of GHRHR over GH1 mutations, POU1F1 over PROP1 mutations and predominance of GHRHR p.Glu72* mutations thus re-affirming the regional diversity in GHD genetics. We report positive and negative predictors of mutations in GHD.

Genetic Anomalies of Growth Hormone Deficiency in Pediatrics

Several different proteins regulate, directly or indirectly, the production of growth hormones from the pituitary gland, thereby complex genetics is involved. Defects in these genes are related to the deficiency of growth hormones solely, or deficiency of other hormones, secreted from the pituitary gland including growth hormones. These studies can aid clinicians to trace the pattern of the disease between the families, start early treatment and predict possible future consequences. This paper highlights some of the most common and novel genetic anomalies concerning growth hormones, which are responsible for various genetic defects in isolated growth and combined pituitary hormone deficiency disease.

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.

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

Isolated growth hormone deficiency (IGHD) is a rare condition mainly caused by mutations in GH1. The aim of this study was to assess the contribution of GHRHR mutations to IGHD in an unusually large group of patients. All GHRHR coding exons and flanking intronic regions were sequenced in 312 unrelated patients with nonsyndromic IGHD. Functional consequences of all newly identified missense variants were assessed in vitro (i.e., study of the expression of recombinant GHRHRs and their ability to activate the cyclic adenosine monophosphate (cAMP) signaling pathway). Genotype-phenotype correlation analyses were performed according to the nature of the identified mutation. We identified 20 different disease-causing GHRHR mutations (truncating and missense loss-of-function mutations), among which 15 are novel, in 24 unrelated patients. Of note, about half (13/24) of those patients represent sporadic cases. The clinical phenotype of patients with at least one missense GHRHR mutation was found to be indistinguishable from that of patients with bi-allelic truncating mutations. This study, which unveils disease-causing GHRHR mutations in 8% (24/312) of IGHD cases, identifies GHRHR as the second IGHD gene most frequently involved after GH1. The finding that 8% of IGHD cases without GH1 mutations are explained by GHRHR molecular defects (including missense mutations), together with the high proportion of sporadic cases among those patients, has important implications for genetic counseling.

Growth Hormone Deficiency in Children: From Suspecting to Diagnosing

Isolated Growth hormone deficiency is an important and treatable cause of short stature. However, it is often difficult to diagnose the condition with certainty due to the lack of a single robust diagnostic test. Short children, other than those with the classical phenotype of immature chubby facies, truncal obesity and micropenis in boys, or those with history of cranial lesions with known association with hypopituitarism, should be evaluated for growth hormone deficiency only after excluding the other more common conditions. These children typically have height markedly below that expected for their midparental height with low height velocity and delayed bone age. Growth hormone levels should be checked by provocative testing, after ensuring that the child is euthyroid, and after priming with sex steroids if indicated. Low levels of Insulin-like growth factor 1 and Insulin-like growth factor binding protein 3 and pituitary abnormalities on neuroimaging provide important corroborative evidence to the diagnosis.

Pathogenic and likely pathogenic genetic alterations and polymorphisms in growth hormone gene (GH1) and growth hormone releasing hormone receptor gene (GHRHR) in a cohort of isolated growth hormone deficient (IGHD) children in Sri Lanka

OBJECTIVE

Genetic alterations in GH1 and GHRHR genes are known to cause isolated growth hormone deficiency (IGHD). Of these, GHRHR codon 72 mutation has been reported to be highly prevalent in the Indian subcontinent, but among Sri Lankans its prevalence was low compared to reports from neighboring countries. The present study was therefore carried out to identify genetic alterations in the GH1 gene and rest of the GHRHR gene in a cohort of Sri Lankan IGHD patients who tested negative for GHRHR codon 72 mutation.

METHODS

Fifty five IGHD children negative for codon 72 (GHRHR) mutation were screened for gross GH1 gene deletion by polymerase chain reaction (PCR) and restriction fragment length polymorphism technique. The coding, intronic and promoter regions of the GH1 gene were sequenced in children who were negative for GH1 deletion (N=53). In a subset (N=40), coding, flanking intronic and promoter regions of the GHRHR gene were screened by single strand conformation polymorphism/sequencing. Identified coding region and intronic variants were subjected to in silico analysis to ascertain pathogenicity. Family members available were screened for the significant variants observed in the index child.

RESULTS

Gross GH1 gene deletions, 6.7kb and 7.0kb were observed in one child each. One novel and 24 reported single nucleotide variants (SNVs) were observed in the GH1 gene and its promoter. These included one reported pathogenic splice site mutation (c.172-2A>T) and one reported likely pathogenic missense mutation (c.406G>T). One large novel deletion of 5875 base pairs that included exon 1, one likely pathogenic novel SNV (c.211G>T) and 18 reported SNVs were observed in the GHRHR gene. Fourteen variants observed were of uncertain significance (8 in GH1 and 6 in GHRHR), twenty three variants were likely benign (11 in GH1 and 12 in GHRHR) and four variants were benign (4 in GH1 and none in GHRHR).

CONCLUSION

In a cohort of IGHD children, six pathogenic or likely pathogenic genetic alterations of either GH1 gene or GHRHR gene were found. These affected a total of six children. Pathogenic status of four of these had been reported in the literature. Novel SNV in the GHRHR gene was predicted to be pathogenic through in silico analysis. The large novel deletion is likely to be pathogenic as it included exon 1 of GHRHR gene. Analysis of other genes will be needed to ascertain the genetic cause of IGHD in the remaining children.

Models of GH deficiency in animal studies

Growth hormone (GH) is a peptide hormone released from pituitary somatotrope cells that promotes growth, cell division and regeneration by acting directly through the GH receptor (GHR), or indirectly via hepatic insulin-like growth factor 1 (IGF1) production. GH deficiency (GHD) can cause severe consequences, such as growth failure, changes in body composition and altered insulin sensitivity, depending of the origin, time of onset (childhood or adulthood) or duration of GHD. The highly variable clinical phenotypes of GHD can now be better understood through research on transgenic and naturally-occurring animal models, which are widely employed to investigate the origin, phenotype, and consequences of GHD, and particularly the underlying mechanisms of metabolic disorders associated to GHD. Here, we reviewed the most salient aspects of GH biology, from somatotrope development to GH actions, linked to certain GHD types, as well as the animal models employed to reproduce these GHD-associated alterations.

Partial Loss of Function of the GHRH Receptor Leads to Mild Growth Hormone Deficiency

OBJECTIVE

Recessive mutations in GHRHR are associated with severe isolated growth hormone deficiency (IGHD), with a final height in untreated patients of 130 cm ± 10 cm (-7.2 ± 1.6 SDS; males) and 114 ± 0.7 cm (-8.3 ± 0.1 SDS; females).

DESIGN

We hypothesized that a consanguineous Pakistani family with IGHD in three siblings (two males, one female) would have mutations in GH1 or GHRHR.

RESULTS

Two novel homozygous missense variants [c.11G>A (p.R4Q), c.236C>T (p.P79L)] at conserved residues were identified in all three siblings. Both were absent from control databases, aside from pR4Q appearing once in heterozygous form in the Exome Aggregation Consortium Browser. The brothers were diagnosed with GH deficiency at 9.8 and 6.0 years (height SDS: -2.24 and -1.23, respectively), with a peak GH of 2.9 μg/liter with low IGF-1/IGF binding protein 3. Their sister presented at 16 years with classic GH deficiency (peak GH <0.1 μg/liter, IGF-1 <3.3 mmol/liter) and attained an untreated near-adult height of 144 cm (-3.0 SDS); the tallest untreated patient with GHRHR mutations reported. An unrelated Pakistani female IGHD patient was also compound homozygous. All patients had a small anterior pituitary on magnetic resonance imaging. Functional analysis revealed a 50% reduction in maximal cAMP response to stimulation with GHRH by the p.R4Q/p.P79L double mutant receptor, with a 100-fold increase in EC50.

CONCLUSION

We report the first coexistence of two novel compound homozygous GHRHR variants in two unrelated pedigrees associated with a partial loss of function. Surprisingly, the patients have a relatively mild IGHD phenotype. Analysis revealed that the pP79L mutation is associated with the compromise in function, with the residual partial activity explaining the mild phenotype.