Association between the Growth Hormone Receptor Exon 3 Polymorphism and Metabolic Factors in Korean Patients with Acromegaly

The Exon 3-Deleted Growth Hormone Receptor (d3GHR) Polymorphism-A Favorable Backdoor Mechanism for the GHR Function

Growth hormone (GH) is a peptide hormone that plays a crucial role in controlling growth, development, and lifespan. Molecular regulation of GH is accomplished via the GH receptor (GHR), which is the main factor influencing human development and is essential to optimal functioning of the GH/IGF-I axis. Two GHR isoforms have been studied, according to the presence (flGHR) or absence (d3GHR) of exon 3. The d3GHR isoform, which lacks exon 3 has recently been related to longevity; individuals carrying this isoform have higher receptor activity, improved signal transduction, and alterations in the treatment response and efficacy compared with those carrying the wild type (WT) isoform (flGHR). Further, studies performed in patients with acromegaly, Prader-Willi syndrome, Turner syndrome, small for gestational age (SGA), and growth hormone deficiency (GHD) suggested that the d3GHR isoform may have an impact on the relationship between GH and IGF-I levels, height, weight, BMI, and other variables. Other research, however, revealed inconsistent results, which might have been caused by confounding factors, including limited sample sizes and different experimental methods. In this review, we lay out the complexity of the GHR isoforms and provide an overview of the major pharmacogenetic research conducted on this ongoing and unresolved subject.

Gender Specificity and Local Socioeconomic Influence on Association of GHR fl/d3 Polymorphism With Growth and Metabolism in Children and Adolescents

OBJECTIVE

Growth hormone receptor (GHR) mediates most GH biological actions. This study is aimed to evaluate whether GHR fl/d3 polymorphism contributes to the inter-individual variability of growth and metabolism in healthy children and adolescents.

METHODS

A total of 4,730 students aged 6-16 years from Yixing and Suqian City in China were included in this cross-sectional study. Height and body mass index (BMI) were transformed into the form of z-score corresponding to age and gender. Logistic regression was used to evaluate the associations of GHR fl/d3 polymorphism with height, BMI, metabolic traits, and hypertension by estimating the odds ratios (ORs) and 95% confidence intervals (CIs).

RESULTS

GHR d3 allele was inversely associated with overweight, total cholesterol (TC) and triglyceride (TG) levels (OR [95% CI] for overweight: 0.754 [0.593-0.959], P = 0.021; OR [95% CI] for TC: 0.744 [0.614-0.902], P = 0.003; OR [95% CI] for TG: 0.812 [0.654-0.998], P = 0.047). GHR d3 allele was associated with decreased odds of pre-hypertension in boys (OR [95% CI]: 0.791 [0.645-0.971], P = 0.025), but associated with increased odds of pre-hypertension and hypertension in girls (ORs [95% CIs]: 1.379 [1.106-1.719], P = 0.004; OR [95% CI]: 1.240 [1.013-1.519], P = 0.037). Interaction of GHR fl/d3 polymorphism with gender contributed to increased odds of pre-hypertension and hypertension (interactive ORs [95% CIs]: 1.735 [1.214-2.481], P = 0.003; OR [95% CI]: 1.509 [1.092-2.086], P = 0.013). Stratification analysis showed that the correlation tendencies of GHR fl/d3 polymorphism and BMI with age were different between two cities with discrepant economic development levels.

CONCLUSION

GHR fl/d3 polymorphism is associated with growth, metabolism, and hypertension in children and adolescents with the gender specificity, and the genetic effect of GHR fl/d3 may be modified by the local socioeconomic levels.

Exon 3-deleted growth hormone receptor isoform is not related to worse bone mineral density or microarchitecture or to increased fracture risk in acromegaly

PURPOSE

Acromegaly is a cause of secondary osteoporosis and is associated with increased risk of vertebral fractures (VFs). The influence of exon 3-deleted isoform of growth hormone receptor (d3-GHR) on bone microarchitecture has not been studied in acromegaly.

AIM

The aim of this study was to analyze the associations between d3-GHR isoform and bone mineral density (BMD), bone microarchitecture, and VFs in acromegaly patients.

METHODS

Consecutive acromegaly patients treated at a single reference center were included. BMD was analyzed using dual-energy X-ray absorptiometry (DXA) and bone microarchitecture was analyzed by high-resolution peripheral quantitative computed tomography (HR-pQCT). The presence of moderate to severe VFs was assessed by thoracic and lumbar X-ray. GHR genotyping was analyzed by PCR, and full-length isoform of GHR (fl-GHR) was represented by a 935-bp fragment and d3-GHR by a 532-bp fragment.

RESULTS

Eighty-nine patients were included [56 females; median age at diagnosis: 43 years (17-78)]. Disease was uncontrolled in 63% of patients. At least one d3-GHR allele was present in 60% of patients. Frequency of active disease (p = 0.276) and hypogonadism (p = 1.000) was not different between patients with fl-GHR and those with at least one d3-GHR. There was no difference in any DXA or HR-pQCT parameters between patients with fl-GHR and those with d3-GHR. Significant VFs were observed in 14% of patients, but there was no difference in frequency between patients with fl-GHR and those with at least one d3-GHR allele (p = 0.578).

CONCLUSIONS

Presence of d3-GHR was not associated with worse BMD or bone microarchitecture or with higher frequency of significant VFs.

MECHANISMS IN ENDOCRINOLOGY: Lessons from growth hormone receptor gene-disrupted mice: are there benefits of endocrine defects?

Growth hormone (GH) is produced primarily by anterior pituitary somatotroph cells. Numerous acute human (h) GH treatment and long-term follow-up studies and extensive use of animal models of GH action have shaped the body of GH research over the past 70 years. Work on the GH receptor (R)-knockout (GHRKO) mice and results of studies on GH-resistant Laron Syndrome (LS) patients have helped define many physiological actions of GH including those dealing with metabolism, obesity, cancer, diabetes, cognition and aging/longevity. In this review, we have discussed several issues dealing with these biological effects of GH and attempt to answer the question of whether decreased GH action may be beneficial.

MECHANISMS IN ENDOCRINOLOGY: Clinical and pharmacogenetic aspects of the growth hormone receptor polymorphism

Pharmacogenetics aims to maximize the beneficial effects of a medical therapy by identifying genetic finger prints from responders and non-responders and, thereby improving safety and efficacy profile of the drug. Most subjects who are deficient in growth hormone (GHD) are candidates for recombinant human GH (rhGH) therapy. To date, it is well established that even after adjustments for several clinical variables, such as age, gender, body composition and the age at onset of the GHD, response to rhGH treatment is highly variable among individuals, part of which is believed to be due to genetic factors within the GH system. As the first genetic variant to potentially influence the individual response to rhGH therapy in children with growth disorders, polymorphism in the GH receptor (GHR) has attracted a great interest as a target for pharmacogenetics. Studies have been conducted to compare the functional and molecular effects of the full-length GHR (fl-GHR) isoform with the exon 3 deleted (d3-GHR) isoform in children and adults treated with rhGH therapy. Additionally, the impact of the GHR polymorphism has been investigated in relation to the clinical status and response to medical treatment in acromegaly, especially to the GHR antagonist drug pegvisomant. We have performed a narrative review of the studies performed to date on the association of GHR polymorphism with rhGH response in children and adults, and its potential influence in the medical management of acromegaly. In addition, data from studies on the general population and in other chronic diseases examining a role of this genetic variant in the regulation of growth and metabolism are summarized.

Frequency of the exon 3-deleted/full-length growth hormone receptor polymorphism in Saudi Arabian population

Objectives:

To investigate the frequency of the growth hormone receptor (GHR)-d3 polymorphism in a random sample of Saudi Arabian population from Jazan province, and test the effects of the polymorphism on some anthropometric factors.

Methods:

This cross-sectional population-based study was conducted during the period from January to April 2017 at the College of Applied Medical Sciences, Jazan University, Southwestern Saudi Arabia. A total of 230 healthy adult male and female volunteers were randomly recruited. Genomic DNA was extracted from the whole blood, and the GHR exon 3 locus was genotyped using multiplex polymerase chain reaction.

Results:

The distributions of the GHR genotypes were as follows: fl/fl (39.1%), fl/d3 (44.8%), and d3/d3 (16.1%). No statistically significant differences were found between fl/fl, fl/d3, or d3/d3 GHR genotypes in terms of weight (p=0.90), height (p=0.12), or body mass index (BMI) (p=0.83) values.

Conclusion:

No correlations were found between the GHR-d3 polymorphism and weight, height, or BMI.