GH receptor isoforms and skeletal fragility in acromegaly

Influence of disease activity and gonadal status on bone mineral density and turnover in acromegaly

INTRODUCTION

The purpose of this study was to evaluate the impact of disease activity and gonadal status on bone mineral density (BMD) and turnover markers (BTMs) in individuals with acromegaly.

MATERIALS AND METHODS

Subjects underwent laboratory tests for PTH, 25-hydroxyvitamin D, calcium, phosphorus, osteocalcin (OC) and C-telopeptide (CTX-1) and bone densitometry at the lumbar spine (LS), femoral neck (FN) and total hip (TH).

RESULTS

Sixty participants (48.6 ± 11.0 years; 66,7% female) were included in this cross-sectional study. Phosphorus, OC, CTX-1, and LS BMD were greater in the active disease group than in the controlled/cured disease group (P = 0.025, P < 0.001, P = 0.007, and P = 0.016, respectively). When analyzing gonadal status, phosphorus, OC and CTX-1 were greater in the hypogonadal group than in the eugonadal group (P = 0.017, P = 0.015, and P = 0.033, respectively). Patients with hypogonadism had a higher prevalence of reduced bone mass compared to eugonadal patients (44 vs. 17%, P = 0.023).

CONCLUSION

This study revealed increased levels of phosphorus and BTMs in patients with active acromegaly. In this group, the greater LS BMD values are likely due to the anabolic effects of GH and IGF-1 and/or to the influence of LS arthropathy. Moreover, hypogonadism negatively impacts bone metabolism in acromegaly, leading to elevated BTMs and a higher prevalence of reduced bone mass in individuals affected by both conditions.

Impact of medical therapy for hormone-secreting Pituitary tumors on bone

PURPOSE

Bone health is often impaired in patients with hormone-secreting pituitary tumors. Since medical therapy is central to their care, understanding how its use impacts on this is highly important.

METHODS

This review summarizes a systemmatic review of the literature on the effects of medical therapies for hormone-secreting pituitary tumors on bone.

RESULTS

In acromegaly, medical therapy lowers bone turnover marker (BTM) levels, consistent with correction of the high bone turnover of active disease, and overall, areal bone mineral density (aBMD) does not change or increases. Somatostatin-receptor ligand (SRL) and pegvisomant-treated acromegaly patients have persistently reduced volumetric BMD and microarchitectural abnormalities of the peripheral skeleton, deficits that are similar to those in surgically-treated patients. Fracture risk remains elevated in medically-treated acromegaly patients but in conjunction with biochemical control the risk is lessened. Treatment of prolactin-secreting tumors with dopamine agonists is associated with improvements in aBMD, but this does not always fully normalize despite effective medical treatment of the prolactinoma. In one cross-sectional study, prolactinoma patients had lower total volumetric BMD and impaired microarchitecture suggesting that bone microstructure does not fully normalize despite dopamine agonist therapy. Cross-sectional studies show a high rate of VF in patients with prolactin-secreting tumors that is lowered on cabergoline therapy, but still the fracture rate of men and postmenopausal women is higher than that of controls in some studies. Studies on the effects of modern-day medical therapy for Cushing's disease on bone are lacking.

CONCLUSION

More research is needed on the effectsof medical therapies for hormone secreting pituitary tumors on bone health.

GH receptor polymorphisms guide second-line therapies to prevent acromegaly skeletal fragility: preliminary results of a pilot study

Background

Skeletal fragility is characterized by increased frequency of vertebral fractures (VFs) in acromegaly. Several trials were conducted to identify modifiable risk factors and predictors of VFs, with limited data on the prognostic role of GH receptor (GHR) isoforms. In this study, we investigated the potential role of GHR polymorphism on the occurrence of incidental VFs (i-VFs), in patients treated with second-line medical therapies.

Methods

A longitudinal, retrospective, observational study was conducted on a cohort of 45 acromegalic patients not-responsive to first-generation somatostatin receptor ligands (fg-SRLs) and treated with GHR antagonist (Pegvisomant) or with the second-generation SRLs (Pasireotide long-acting release).

Results

Second line treatments were Pegvisomant plus fg-SRLs in 26 patients and Pasireotide LAR in 19 patients. From the group treated with fg-SRLs+Peg-V, the fl-GHR isoform was identified in 18 patients (69.2%) and the d3-GHR isoform in 8 patients (30.8%). I-VFs arose exclusively in fl-GHR isoform carriers (p=0.039). From the group treated with Pasireotide LAR, the fl-GHR isoform was identified in 11 patients (57.9%), and the d3-GHR isoform in 8 patients (42.1%). I-VFs arose exclusively in d3-GHR isoform carriers (p=0.018). Patients with fl-GHR isoform had a higher risk for i-VFs if treated with fg-SRL+Peg-V (OR: 1.6 95%IC: 1.1-2.3, p=0.04), and a lower risk if treated with Pasi-LAR (OR: 0.26 IC95%: 0.11-0.66, p=0.038).

Conclusions

Our data support a predictive role of the GHR isoforms for the occurrence of i-VFs in acromegalic patients treated with second-line drugs, tailored to the individual patient. The knowledge of the GHR polymorphism may facilitate the choice of second-line therapies, improving the therapeutic approach, in the context of personalized medicine.

Bone health and skeletal fragility in second- and third-line medical therapies for acromegaly: preliminary results from a pilot single center experience

INTRODUCTION

Skeletal fragility is a clinically relevant and not-reversible complication of acromegaly, involving around 30-40% of patients since the disease diagnosis. Few studies have investigated the effects on skeletal health of medical therapies for acromegaly. In this retrospective longitudinal monocentre study, we investigated the outcome of skeletal fragility in patients treated with Pasireotide Lar in combination with Pegvisomant (Pasi-Lar + Peg-V), also comparing those observed in patients treated with conventional therapies.

RESULTS

We included 6 patients treated with Pasi-Lar + Peg-V, 5 patients treated with Peg-V in monotherapy (m-Peg-V), 16 patients treated with Peg-V plus first-generation somatostatin receptor ligands (fg-SRLs + Peg-V), 9 patients treated with Pasi-Lar. None of the patients treated with Pasi-Lar + Peg-V experienced worsening of spine and femoral bone mineral density (BMD) and incident vertebral fractures (i-VFs). Eight patients experienced i-VFs. The frequency of i-VFs was significantly lower in patients treated with the Pasi-Lar + Peg-V (0/8; 0%), as compared to those observed in m-Peg-V treated patients (4/8; 50%, p = 0.02). The frequency of i-VFs was slightly but not significantly higher in Pasi-Lar treated patients (1/8; 12.5% p = 0.6) and in fg-SRLs + Peg-V treated patients (3/8; 37.5% p = 0.364), concerning those treated with Pasi-Lar + Peg-V (0/8; 0%). I-VFs occurred more frequently in patients with higher GH levels at acromegaly diagnosis (p < 0.001), and in patients who experienced a BMD worsening (p = 0.005).

CONCLUSION

Our preliminary data suggested that in conventional and multi-drug resistant acromegaly, the combination therapy Pasi-Lar + Peg-V may prevent the worsening of BMD and the occurrence of i-VFs. Prospective and translational studies should further validate these results and ascertain underlying physiopathology mechanisms.

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.

Vertebral Fractures in Acromegaly: A Systematic Review

INTRODUCTION

Acromegaly is characterized by a very particular alteration of bone microarchitecture, leading to increased vertebral fragility. However, due to inconsistent and insufficient evidence, no guidelines are available for the evaluation of this osteopathy.

METHODS

We performed a literature review of studies published between 1968 and January 2022 on the PubMed and SCOPUS databases using the terms "acromegaly" and "vertebral fractures". Twenty-four studies were found eligible for inclusion, published between June 2005 and November 2021. Included studies evaluated acromegaly patients, who were assessed for the presence of vertebral fractures. We excluded case reports, reviews, meta-analyses, letters to the editor, articles not written in English, and research performed on the same set of patients without significant differences in study design. Risk of bias was avoided by following the ROBIS risk of bias recommendations. We executed rigorous data collection, and the results are depicted as a narrative overview, but also, as statistical synthesis. Limitations of the evidence presented in the study include study heterogeneity, small sample sizes, and a small number of prospective studies with short follow-up.

FINDINGS

Data regarding vertebral fractures (VFs) in acromegaly and their influencing factors are variable. Twenty-four studies were included, nine out of which had a prospective design. The smallest group of acromegaly patients had 18 subjects and the largest included 248 patients. Prevalence ranges between 6.5% and 87.1%, although most studies agree that it is significantly higher than in controls. VFs also have a higher incidence (between 5.6% and 42%) and are more frequently multiple (between 46.15% and 71%). Evidence shows that disease activity and active disease duration are influencing factors for the prevalence and incidence of VFs. Nonetheless, hypogonadism does not seem to influence the frequency of VFs. While reports are conflicting regarding the use of bone mineral density in acromegaly, evidence seems to be slightly in favor of it not being associated with VFs. However, trabecular bone score is significantly lower in fractured patients, although no prospective studies are available.

INTERPRETATION

Vertebral fractures evaluation should be performed with regularity in all acromegalic patients, especially in the presence of active disease. Disease activity is an important determinant of vertebral fracture incidence and prevalence, although hypogonadism is less so. To clarify the predictive value of both BMD and TBS for vertebral fractures, additional, larger, prospective studies are necessary.

Impact of the diagnostic delay of acromegaly on bone health: data from a real life and long term follow-up experience

INTRODUCTION

Acromegaly is a chronic disease with systemic complications. Disease onset is insidious and consequently typically burdened by diagnostic delay. A longer diagnostic delay induces more frequently cardiovascular, respiratory, metabolic, neuropsychiatric and musculoskeletal comorbidities. No data are available on the effect of diagnostic delay on skeletal fragility. We aimed to evaluate the effect of diagnostic delay on the frequency of incident and prevalent of vertebral fractures (i-VFs and p-VFs) in a large cohort of acromegaly patients.

PATIENTS AND METHODS

A longitudinal, retrospective and multicenter study was conducted on 172 acromegaly patients.

RESULTS

Median diagnostic delay and duration of follow-up were respectively 10 years (IQR: 6) and 10 years (IQR: 8). P-VFs were observed in 18.6% and i-VFs occurred in 34.3% of patients. The median estimated diagnostic delay was longer in patients with i-VFs (median: 11 years, IQR: 3), in comparison to those without i-VFs (median: 8 years, IQR: 7; p = 0.02). Age at acromegaly diagnosis and at last follow-up were higher in patients with i-VFs, with respect to those without i-VFs. The age at acromegaly diagnosis was positively associated with the diagnostic delay (p < 0.001, r = 0.216). A longer history of active acromegaly was associated with a high frequency of i-VFs (p = 0.03). The logistic regression confirmed that patients with a diagnostic delay > 10 years had 1.5-folds increased risk of developing i-VFs (OR: 1.5; 95%CI: 1.1-2; p = 0.017).

CONCLUSION

Our data showed that the diagnostic delay in acromegaly has a significant impact on VF risk, further supporting the clinical relevance of an early acromegaly diagnosis.

Update on vertebral fractures in pituitary diseases: from research to clinical practice

Derangement of pituitary hormone axes can induce changes in bone remodeling and metabolism with possible alterations in bone microarchitectural structure and increased susceptibility to fractures. Vertebral fractures (VFs), which are a hallmark of skeletal fragility, have been described in a very large number of patients with pituitary diseases. These fractures are clinically relevant, since they predispose to further fractures and may negatively impact on patients' quality of life. However, the management of skeletal fragility and VFs in the specific setting of pituitary diseases is a challenge, since the awareness for this disease is still low, prediction of VFs is uncertain, the diagnosis of VFs cannot be solely based on a clinical approach and also needs a radiological and morphometric approach, the risk of fractures may not be decreased via treatment of pituitary hormone disorders, and the effectiveness of bone-active drugs in this setting is not always evidence-based. This review is an update on skeletal fragility in patients with pituitary diseases, with a focus on clinical and therapeutic aspects concerning the management of VFs.

Acromegaly is associated with vertebral deformations but not vertebral fractures: Results of a cross-sectional monocentric study

OBJECTIVES

Patients with acromegaly appear to be at increased risk of vertebral fractures despite normal bone mineral density. We investigated the prevalence of vertebral fractures in a cohort of acromegalic patients under 80 years of age.

METHODS

Monocentric cross-sectional study performed at Nantes University Hospital from 1988 to 2018. Fifty patients (18 females, 32 males) with a median age of 52.3 years (range: 27-78) were included. Radiological vertebral fractures were evaluated on conventional lumbar and thoracic spine radiographs using Genant's semiquantitative fracture assessment. We studied qualitative abnormalities of the spine using three criteria: osteophytes, disc-space narrowing and wedge-shaped vertebrae. We analysed bone mineral density and endocrine status.

RESULTS

Three patients (6%) had a vertebral fracture: one grade 1 and two grade 2 according to Genant's assessment, with two osteoporotic and one osteopenic patients. They had no unsubstituted pituitary deficiency. Considering the frank deformations (osteophyte or disc narrowing≥grade 2 or wedge-shaped), the thoracic spine was deformed in 22 patients (44%) and the lumbar spine in 21 patients (42%).

CONCLUSION

Acromegalic patients had a low prevalence of vertebral fractures but had a significant amount of vertebral deformations. We speculate that this high prevalence of frank deformations could explain the previously reported high prevalence of vertebral fractures.

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.

Systemic Complications of Acromegaly and the Impact of the Current Treatment Landscape: An Update

Acromegaly is a chronic systemic disease with many complications and is associated with increased mortality when not adequately treated. Substantial advances in acromegaly treatment, as well as in the treatment of many of its complications, mainly diabetes mellitus, heart failure, and arterial hypertension, were achieved in the last decades. These developments allowed change in both prevalence and severity of some acromegaly complications and furthermore resulted in a reduction of mortality. Currently, mortality seems to be similar to the general population in adequately treated patients with acromegaly. In this review, we update the knowledge in complications of acromegaly and detail the effects of different acromegaly treatment options on these complications. Incidence of mortality, its correlation with GH (cumulative exposure vs last value), and IGF-I levels and the shift in the main cause of mortality in patients with acromegaly are also addressed.

Pituitary Diseases and Bone

Neuroendocrinology of bone is a new area of research based on the evidence that pituitary hormones may directly modulate bone remodeling and metabolism. Skeletal fragility associated with high risk of fractures is a common complication of several pituitary diseases such as hypopituitarism, Cushing disease, acromegaly, and hyperprolactinemia. As in other forms of secondary osteoporosis, pituitary diseases generally affect bone quality more than bone quantity, and fractures may occur even in the presence of normal or low-normal bone mineral density as measured by dual-energy X-ray absorptiometry, making difficult the prediction of fractures in these clinical settings. Treatment of pituitary hormone excess and deficiency generally improves skeletal health, although some patients remain at high risk of fractures, and treatment with bone-active drugs may become mandatory. The aim of this review is to discuss the physiological, pathophysiological, and clinical insights of bone involvement in pituitary diseases.

Prevalence of morphometric vertebral fractures in "difficult" patients with acromegaly with different biochemical outcomes after multimodal treatment

INTRODUCTION

Skeletal fragility with high risk of vertebral fractures is an emerging complication of acromegaly in close relationship with duration of active disease. The aim of this cross-sectional study was to evaluate the prevalence and determinants of vertebral fractures in males and females with a history of long-standing active acromegaly undergoing treatment with Pegvisomant.

SUBJECTS AND METHODS

Thirty-eight patients (25 females, 13 males) with acromegaly under Pegvisomant therapy were evaluated for vertebral fractures and bone mineral density at lumbar spine and femoral neck. Gonadal status, serum IGF1 levels and growth hormone receptor genotype were also assessed.

RESULTS

Vertebral fractures were detected in 12 patients (31.6%). Fractured patients had longer duration of active disease (p = 0.01) with higher frequency of active acromegaly (p = 0.04), received higher dose of Pegvisomant (p = 0.008), and were more frequently hypogonadic (p = 0.02) as compared to patients who did not fracture. Stratifying the patients for gender, vertebral fractures were significantly associated with Pegvisomant dose (p = 0.02) and untreated hypogonadism (p = 0.02) in males and with activity of disease (p = 0.03), serum insulin-like growth factor-I values (p = 0.01) and d3GHR polymorphism (p = 0.005) in females. No significant association was found between vertebral fractures and bone mineral density at either skeletal site.

CONCLUSION

Vertebral fractures are a frequent complication of long-standing active acromegaly. When patients are treated with Pegvisomant, vertebral fractures may occur in close relationship with active acromegaly and coexistent untreated hypogonadism.

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.

Calcium and Bone Turnover Markers in Acromegaly: A Prospective, Controlled Study

CONTEXT

Acromegaly has been associated with calcium-phosphate and bone turnover alterations. Controlled studies of these interactions are sparse.

OBJECTIVE

To evaluate calcium and bone metabolism in active and treated acromegaly.

DESIGN/SETTING/PATIENTS

We conducted a controlled, prospective study at a tertiary referral center. We studied 22 patients with acromegaly referred for surgical or medical therapy (ACM) and 22 with nonfunctioning pituitary adenomas referred for surgery (control).

MAIN OUTCOME MEASURES

Calcium (serum and urine), phosphorus, parathyroid hormone (PTH), 25-hydroxy- and 1,25-dihydroxy-vitamin D, bone turnover markers [serum C-terminal telopeptide of type 1 collagen (CTX) and procollagen type 1 N-terminal propeptide (P1NP)], and cytokines [receptor activator of nuclear factor κB ligand (RANK-L) and osteoprotegerin (OPG)] at baseline and 3 to 6 months after treatment.

RESULTS

At baseline, the ACM group had lower PTH levels than controls (36.3 ± 13.9 pg/mL vs 56.0 ± 19.9 pg/mL) and higher phosphorus (4.34 ± 0.71 mg/dL vs 3.55 ± 0.50 mg/dL) (P < 0.01). Groups had similar levels of serum and urine calcium and 25-hydroxy- and 1,25-dihydroxy-vitamin D. The ACM group had higher bone turnover markers than control; P1NP and CTX were strongly correlated (r2 = 0.82, P < 0.05). CTX was dependent on age and disease group but not on sex or gonadal status. After treatment of acromegaly, serum calcium (9.52 ± 0.43 mg/dL to 9.26 ± 0.28 mg/dL), phosphorus (4.34 ± 0.71 mg/dL to 3.90 ± 0.80 mg/dL), and CTX (0.91 ± 0.75 ng/mL to 0.63 ± 0.68 ng/mL) decreased, while PTH increased (36.3 ± 13.9 pg/mL to 48.9 ± 16.7 pg/mL) (P < 0.01). 25-hydroxy-vitamin D, P1NP, and RANK-L/OPG ratio did not change significantly.

CONCLUSION

Acromegaly patients exhibited PTH-independent calcium-phosphate alterations and enhanced coupled bone formation and resorption. Within 6 months of treatment, bone resorption decreased, whereas RANK-L/OPG changes were inconsistent.

Growth hormone receptor isoforms and fracture risk in adult-onset growth hormone-deficient patients

INTRODUCTION

Growth hormone deficiency is considered the most important factor determining skeletal fragility in hypopituitary patients. Osteoblasts and chondrocytes express growth hormone (GH) receptor. Two GH receptor isoforms (GHRi) have been identified: they differ for the presence/absence of a protein fragment encoded by exon 3 of GHR gene. Consequently, three genotypes were identified: carriers of both the full-length proteins (flfl-GHR), carriers of one full-length protein and one deleted protein (fld3-GHR) and carriers of both deleted proteins (d3d3-GHR). This polymorphism confers a higher sensitivity to endogenous GH and to recombinant human GH (rhGH); its effect on bone metabolism and skeletal fragility is unknown. The aim of this article was to investigate the role of GHRi in predicting skeletal fragility in adult-onset GHD (AO-GHD) patients.

SUBJECTS AND METHODS

A cross-sectional study was conducted to investigate the association between the d3-GHR isoform and the prevalence of morphometric vertebral fractures (VFs) in AO-GHD. Ninety-three AO-GHD were enrolled. Forty-nine patients carried flfl-GHRi (52·7%), and 44 patients (47·3%) carried at least one allele of the d3-GHR isoform. Thirty-two VFs were documented. Fifty-seven patients underwent rhGH replacement therapy.

RESULTS

Median age was significantly higher in fractured patients as compared to nonfractured ones; d3-carrier patients showed a lower VF risk as compared to flfl-GHRi (OR: 0·37, 95% IC: 0·24-0·55, P < 0·0001). This finding was also confirmed in AO-GHD undergoing rhGH replacement therapy.

CONCLUSION

This study suggests that d3-GHR may protect AO-GHD particularly when treated with rhGH from the risk of VFs.

Skeletal effects of growth hormone and insulin-like growth factor-I therapy

The growth hormone/insulin-like growth factor (GH/IGF) axis is critically important for the regulation of bone formation, and deficiencies in this system have been shown to contribute to the development of osteoporosis and other diseases of low bone mass. The GH/IGF axis is regulated by a complex set of hormonal and local factors which can act to regulate this system at the level of the ligands, receptors, IGF binding proteins (IGFBPs), or IGFBP proteases. A combination of in vitro studies, transgenic animal models, and clinical human investigations has provided ample evidence of the importance of the endocrine and local actions of both GH and IGF-I, the two major components of the GH/IGF axis, in skeletal growth and maintenance. GH- and IGF-based therapies provide a useful avenue of approach for the prevention and treatment of diseases such as osteoporosis.

Growth hormone receptor exon 3 isoforms may have no importance in the clinical setting of multiethnic Brazilian acromegaly patients

BACKGROUND

Acromegaly is associated with significant morbidity and increased mortality, but has a variable severity phenotype. The presence of the exon 3-deleted isoform of the growth hormone receptor (d3-GHR) may influence the disease phenotype and treatment outcomes, including the frequency of biochemical discordance after medical treatment.

AIMS

The objective of this study was to analyze the influence of the d3-GHR isoform on clinical and biochemical characteristics and in the treatment outcomes of Brazilian multiethnic acromegaly patients.

METHODS

We retrospectively analyzed our acromegaly outpatient clinic databank and collected demographic, clinical, biochemical and treatment outcome data from those patients who agreed to participate in the study. A blood sample was collected from all patients, the DNA was extracted and the GHR isoforms were evaluated by PCR, with the full length (fl)-GHR represented by a 935-bp fragment and the d3-GHR represented by a 532-bp fragment.

RESULTS

A total of 121 patients were included. Fifty-six patients (46.3 %) were full-length homozygous (fl/fl), 48 (39.7 %) were heterozygous (fl/d3) and 17 (14.0 %) were d3-GHR homozygous (d3/d3). There was no difference between patients homozygous for the fl isoform and those harboring at least one d3-GHR allele in the demographic, clinical and biochemical data or in the treatment outcomes, including somatostatin receptor ligands (SRL) monotherapy, combination therapy with SRL and cabergoline and pegvisomant treatment. There was also no difference between the groups for the frequency of GH and IGF-I discordance after medical treatment.

CONCLUSION

GHR exon 3 genotyping appears to have no clinical significance, at least in Brazilian acromegaly patients.

Understanding the effect of acromegaly on the human skeleton

Acromegaly, caused in most cases by Growth Hormone (GH)-secreting pituitary adenomas, is characterized by increased skeletal growth and enlargement of the soft tissue, because GH and its effector Insulin-like Growth factor-1 are important regulators of bone homeostasis and have a central role in the longitudinal bone growth and maintenance of bone mass. Areas covered: Despite the anabolic effect of these hormones is well known, as a result of the stimulation of bone turnover and especially of bone formation, many acromegalic patients are suffering from a form of secondary osteoporosis with increased risk of fractures. Expert commentary: In this review, we summarize the pathophysiology, diagnosis, clinical picture, disease course and management of skeletal complications of acromegaly, focusing in particular on secondary osteoporosis and fracture risk in acromegaly.

Genetic Predictors of Response to Different Medical Therapies in Acromegaly

In the era of predictive medicine, management of diseases is evolving into a more personal and individualized approach, as more data are available regarding clinical, biochemical, radiological, molecular, histopathological, and genetic aspects. In the particular setting of acromegaly, which is a rare, chronic, debilitating, and disfiguring disease, an optimized approach deems even more necessary, especially because of an associated increased morbidity and mortality, the impact on patients' quality of life, and the increased cost of frequently necessary life-long treatments. In this paper, we review the available studies that address potential genetic influences on acromegaly, their role in the outcome, and response to treatments, as well as their contribution to the risk of developing side effects. We focus mainly on pharmacogenetic factors involved during treatment with dopamine agonists, somatostatin analogs, and pegvisomant. Specifically, mutations in dopamine receptors, somatostatin receptors, growth hormone receptors, and metabolic pathways involved in growth hormone action; polymorphisms in the insulin-like growth factor and the insulin-like growth factor binding proteins; and polymorphisms in other genes that may determine differences in the frequency of developing adverse events.

Effects of Growth Hormone on Bone

PURPOSE

Describe the effects of growth hormone (GH) and insulin-like growth factor 1 (IGF-1) on the skeleton.

FINDINGS

The GH and IGF-1 axis has pleiotropic effects on the skeleton throughout the lifespan by influencing bone formation and resorption. GH deficiency leads to decreased bone turnover, delayed statural growth in children, low bone mass, and increased fracture risk in adults. GH replacement improves adult stature in GH deficient children, increases bone mineral density (BMD) in adults, and helps to optimize peak bone acquisition in patients, during the transition from adolescence to adulthood, who have persistent GH deficiency. Observational studies suggest that GH replacement may mitigate the excessive fracture risk associated with GH deficiency. Acromegaly, a state of GH and IGF-1 excess, is associated with increased bone turnover and decreased BMD in the lumbar spine observed in some studies, particularly in patients with hypogonadism. In addition, patients with acromegaly appear to be at an increased risk of morphometric-vertebral fractures, especially in the presence of active disease or concurrent hypogonadism. GH therapy also has beneficial effects on statural growth in several conditions characterized by GH insensitivity, including chronic renal failure, Turner syndrome, Prader-Willi syndrome, postnatal growth delay in patients with intrauterine growth retardation who do not demonstrate catchup growth, idiopathic short stature, short stature homeobox-containing (SHOX) gene mutations, and Noonan syndrome.

SUMMARY

GH and IGF-1 have important roles in skeletal physiology, and GH has an important therapeutic role in both GH deficiency and insensitivity states.

Rapid method for growth hormone receptor exon 3 delete (GHRd3) SNP genotyping from archival human placental samples

Analysis of archival samples from cohorts of pregnant women may be key to discovering prognosticators of stillbirth and pregnancy/perinatal complications. Growth hormone (GH) and its receptor (GHR) are pivotal in feto-placental development and pregnancy maintenance. We report a rapid, optimized method for genotyping the GHR full-length versus exon 3-deleted isoform (GHRd3). TaqMan single nucleotide polymorphism (SNP) genotyping proved superior to standard multiplex polymerase chain reaction (PCR) in allele detection and GHR genotyping from archived samples, including those with poor genomic deoxyribonucleic acid quality/quantity such as formalin fixed, paraffin embedded, blood, and serum. Furthermore, this assay is suitable for high through put 96 or 384-well plate quantitative PCR machines with automated genotype calling software. The TaqMan genotyping assay can increase the data obtained from precious archival human samples.

Excessive growth hormone expression in male GH transgenic mice adversely alters bone architecture and mechanical strength

Patients with acromegaly have a higher prevalence of vertebral fractures despite normal bone mineral density (BMD), suggesting that GH overexpression has adverse effects on skeletal architecture and strength. We used giant bovine GH (bGH) transgenic mice to analyze the effects of high serum GH levels on BMD, architecture, and mechanical strength. Five-month-old hemizygous male bGH mice were compared with age- and sex-matched nontransgenic littermates controls (NT; n=16/group). Bone architecture and BMD were analyzed in tibia and lumbar vertebrae using microcomputed tomography. Femora were tested to failure using three-point bending and bone cellular activity determined by bone histomorphometry. bGH transgenic mice displayed significant increases in body weight and bone lengths. bGH tibia showed decreases in trabecular bone volume fraction, thickness, and number compared with NT ones, whereas trabecular pattern factor and structure model index were significantly increased, indicating deterioration in bone structure. Although cortical tissue perimeter was increased in transgenic mice, cortical thickness was reduced. bGH mice showed similar trabecular BMD but reduced trabecular thickness in lumbar vertebra relative to controls. Cortical BMD and thickness were significantly reduced in bGH lumbar vertebra. Mechanical testing of femora confirmed that bGH femora have decreased intrinsic mechanical properties compared with NT ones. Bone turnover is increased in favor of bone resorption in bGH tibia and vertebra compared with controls, and serum PTH levels is also enhanced in bGH mice. These data collectively suggest that high serum GH levels negatively affect bone architecture and quality at multiple skeletal sites.

Acromegaly and bone disease

PURPOSE OF REVIEW

To provide an update on current understanding of osteoporosis associated with acromegaly.

RECENT FINDINGS

Patients with acromegaly have an increased risk of morphometric vertebral fractures. This seems to correlate with acromegaly activity and its duration, but it persists after biochemical control is achieved. Coexistent hypogonadism, diabetes mellitus and over-replacement with glucocorticoids have additional detrimental effects. Bone mineral density can be normal, increased or decreased, and is usually discordant with occurrence of fractures. However, a decrease in the hip bone mineral density during follow-up has been associated with development of new vertebral fractures. Bone turnover markers are increased and tend to normalize after biochemical control of acromegaly. Hypercalcemia rarely occurs in acromegaly and may be parathyroid hormone-dependent or 1,25 dihydroxy-vitamin D dependent. The latter improves with biochemical control of acromegaly.

SUMMARY

Screening with thoracic and lumbar vertebral radiographs is indicated in patients with acromegaly. We recommend biochemical control of acromegaly, treatment of hypogonadism and other risk factors of osteoporosis and avoiding supraphysiologic doses of glucocorticoids. Further studies are needed to understand mechanisms of skeletal fragility in acromegaly and clinical impact of vertebral fractures. Further studies of tailored therapy for patients with acromegaly and osteoporosis are also needed.