Effects of growth hormone (GH) and insulin-like growth factor-I therapy in patients with gene defects in the GH axis

Effects of Growth Hormone on Adult Human Gonads: Action on Reproduction and Sexual Function

Growth hormone (GH), which is commonly considered to be a promoter of growth and development, has direct and indirect effects on adult gonads that influence reproduction and sexual function of humans and nonhumans. GH receptors are expressed in adult gonads in some species including humans. For males, GH can improve the sensitivity of gonadotropins, contribute to testicular steroidogenesis, influence spermatogenesis possibly, and regulate erectile function. For females, GH can modulate ovarian steroidogenesis and ovarian angiogenesis, promote the development of ovarian cells, enhance the metabolism and proliferation of endometrial cells, and ameliorate female sexual function. Insulin-like growth factor-1 (IGF-1) is the main mediator of GH. In vivo, a number of the physiological effects of GH are mediated by GH-induced hepatic IGF-1 and local IGF-1. In this review, we highlight the roles of GH and IGF-1 in adult human gonads, clarify potential mechanisms, and explore the efficacy and the risk of GH supplementation in associated deficiency and assisted reproductive technologies. Besides, the effects of excess GH on adult human gonads are discussed as well.

Novel Insights Into the Genetic Causes of Short Stature in Children

Short stature is a common reason for consulting a growth specialist during childhood. Normal height is a polygenic trait involving a complex interaction between hormonal, nutritional and psychosocial components. Genetic factors are becoming very important in the understanding of short stature. After exclusion of the most frequent causes of growth failure, clinicians need to evaluate whether a genetic cause might be taken into consideration. In fact, genetic causes of short stature are probably misdiagnosed during clinical practice and the underlying cause of short stature frequently remains unknown, thus classifying children as having idiopathic short stature (ISS). However, over the past decade, novel genetic techniques have led to the discovery of novel genes associated with linear growth and thus to the ability to define new possible aetiologies of short stature. In fact, thanks to the newer genetic advances, it is possible to properly re-classify about 25–40% of children previously diagnosed with ISS. The purpose of this article is to describe the main monogenic causes of short stature, which, thanks to advances in molecular genetics, are assuming an increasingly important role in the clinical approach to short children.

Biological Significance of Anti-GH Antibodies in Children Treated with rhGH

BACKGROUND

The occurrence of antidrug antibodies is common in children treated with recombinant human growth hormone (rhGH). However, their clinical significance is unclear.

OBJECTIVE

This study aimed to examine the clinical significance of anti-GH antibodies by analyzing the phenotype of patients who tested positive in relation to the quantity of anti-GH antibodies.

METHOD

In this laboratory-based retrospective study encompassing a time span of 6 years, all positive samples were identified, and senders were contacted. Anti-GH antibodies were measured using a radioprecipitation assay; positive samples underwent a confirmatory assay.

RESULTS

Out of a total of 104 samples from 66 patients, positive test results were found in 28 samples from 13 patients. Clinical data were available from all but one. The group with positive test results comprised 6 patients with a normal response to GH provocative tests (group A) and 6 with an insufficient response or with isolated GH deficiency (IGHD) type 1A (group B). Diagnoses in group A were neurosecretory dysfunction, bioinactive GH syndrome and constitutional delay of growth and puberty. Diagnoses in group B were IGHD type 1A, septo-optic dysplasia, and cerebral midline defect with multiple pituitary hormone deficiency. Insufficient growth response to rhGH was absent except in one sibling pair with IGHD type 1A and a patient with cerebral midline defect. These patients had the highest concentrations of anti-GH antibodies.

CONCLUSIONS

The biological significance of anti-GH antibodies seems to be limited to patients with high concentrations of anti-GH antibodies. For all other patients, we recommend a careful "wait and see" strategy and monitoring antibody titers.

Clinical challenges in the management of isolated GH deficiency type IA in adulthood

Isolated GH deficiency type IA (IGHDIA) is an infrequent cause of severe congenital GHD, often managed by pediatric endocrinologists, and hence few cases in adulthood have been reported. Herein, we describe the clinical status of a 56-year-old male with IGHDIA due to a 6.7 kb deletion in GH1 gene that encodes GH, located on chromosome 17. We also describe phenotypic and biochemical parameters, as well as characterization of anti-GH antibodies after a new attempt made to treat with GH. The height of the adult patient was 123 cm. He presented with type 2 diabetes mellitus, dyslipidemia, osteoporosis, and low physical and psychological performance, compatible with GHD symptomatology. Anti-GH antibodies in high titers and with binding activity (>101 IU/ml) were found 50 years after exposure to exogenous GH, and their levels increased significantly (>200 U/ml) after a 3-month course of 0.2 mg/day recombinant human GH (rhGH) treatment. Higher doses of rhGH (1 mg daily) did not overcome the blockade, and no change in undetectable IGF1 levels was observed (<25 ng/ml). IGHDIA patients need lifelong medical surveillance, focusing mainly on metabolic disturbances, bone status, cardiovascular disease, and psychological support. Multifactorial conventional therapy focusing on each issue is recommended, as anti-GH antibodies may inactivate specific treatment with exogenous GH. After consideration of potential adverse effects, rhIGF1 treatment, even theoretically indicated, has not been considered in our patient yet.

LEARNING POINTS

Severe isolated GHD may be caused by mutations in GH1 gene, mainly a 6.7 kb deletion.Appearance of neutralizing anti-GH antibodies upon recombinant GH treatment is a characteristic feature of IGHDIA.Recombinant human IGF1 treatment has been tested in children with IGHDIA with variable results in height and secondary adverse effects, but any occurrence in adult patients has not been reported yet.Metabolic disturbances (diabetes and hyperlipidemia) and osteoporosis should be monitored and properly treated to minimize cardiovascular disease and fracture risk.Cerebral magnetic resonance imaging should be repeated in adulthood to detect morphological abnormalities that may have developed with time, as well as pituitary hormones periodically assessed.

Development of antibodies against growth hormone (GH) during rhGH therapy in a girl with idiopathic GH deficiency: a case report

A 12.5-year-old Italian girl was referred to our institute for progressive growth failure from the age of 6 years, with a height of 128.2 cm (-3.37 SDS) and a bone age of 9 years. Endocrinological evaluation revealed a partial growth hormone deficiency (GHD) and GH therapy was started at a dosage of 0.25 mg/kg/week. During the first 3 years, she showed an increase in growth rate and experienced pubertal development onset. Then a poor growth rate (2 cm/year=0.43 SDS) was observed, notwithstanding an increase in GH dosage (0.35 mg/kg/week) and good compliance. We found a positive anti-GH antibody titre (1:1850, cutoff 1/100), confirmed 6 months later (1:2035); the antibodies had low binding capacity (0.63 μg/mL) and were only partially capable of inhibiting the GH effect. However, GH treatment was discontinued, and after 3 months the antibody titre decreased (1:950). In conclusion, we suggest evaluation of anti-GH antibodies in GH-treated idiopathic GHD children in whom growth response decreases after some years of therapy.

Predicting response to growth hormone treatment

Despite extensive experience over the past 25 y in managing growth failure with growth hormone (rhGH), predicting treatment efficacy in individual children remains a challenge. In this paper, the authors present the methods that are currently available to clinicians for predicting the growth response, and other more sophisticated techniques which have the potential to pave the way for individualised therapy in the future.

Genetic Defects in the Growth Hormone-IGF-I Axis Causing Growth Hormone Insensitivity and Impaired Linear Growth

Human genetic defects in the growth hormone (GH)-IGF-I axis affecting the IGF system present with growth failure as their principal clinical feature. This is usually associated with GH insensitivity (GHI) presenting in childhood as severe or mild short stature. Dysmorphic features and metabolic abnormalities may also be present. The field of GHI due to mutations affecting GH action has evolved rapidly since the first description of the extreme phenotype related to homozygous GH receptor (GHR) mutations in 1966. A continuum of genetic, phenotypic, and biochemical abnormalities can be defined associated with clinically relevant defects in linear growth. The mechanisms of the GH-IGF-I axis in the regulation of normal human growth is discussed followed by descriptions of mutations in GHR, STAT5B, IGF-I, IGFALS, IGF1R, and GH1 defects causing bio-inactive GH or anti-GH antibodies. These GH-IGF-I axis defects are associated with a range of clinical, and hormonal characteristics. An up-dated approach to the clinical assessment of the patient with GHI focusing on investigation of the GH-IGF-I axis and relevant molecular studies contributing to the identification of causative genetic defects is also discussed.

Evidence for a continuum of genetic, phenotypic, and biochemical abnormalities in children with growth hormone insensitivity

GH insensitivity (GHI) presents in childhood as growth failure and in its severe form is associated with dysmorphic and metabolic abnormalities. GHI may be caused by genetic defects in the GH-IGF-I axis or by acquired states such as chronic illness. This article discusses the former category. The field of GHI due to mutations affecting GH action has evolved considerably since the original description of the extreme phenotype related to homozygous GH receptor (GHR) mutations over 40 yr ago. A continuum of genetic, phenotypic, and biochemical abnormalities can be defined associated with clinically relevant defects in linear growth. The role and mechanisms of the GH-IGF-I axis in normal human growth is discussed, followed by descriptions of mutations in GHR, STAT5B, PTPN11, IGF1, IGFALS, IGF1R, and GH1 defects causing bioinactive GH or anti-GH antibodies. These defects are associated with a range of genetic, clinical, and hormonal characteristics. Genetic abnormalities causing growth failure that is less severe than the extreme phenotype are emphasized, together with an analysis of height and serum IGF-I across the spectrum of different types of GHR defects. An overall view of genotype and phenotype relationships is presented, together with an updated approach to the assessment of the patient with GHI, focusing on investigation of the GH-IGF-I axis and relevant molecular studies contributing to this diagnosis.

Insulin-like growth factor-I deficiency in children with growth hormone insensitivity: current and future treatment options

Growth hormone (GH) acts directly at the growth plate and through the production of insulin-like growth factor (IGF)-I. At least 50% of the hormone circulates bound to GH binding protein, and its secretion is controlled by growth hormone-releasing hormone and somatostatin. Once GH binds to two GH receptors, the janus activated kinase/signal transducers and activators of transcription (JAK/STAT) protein pathway is activated, resulting in the production of IGF-I. Serum IGF-I is produced predominantly in the liver and circulates in a 140 kDa complex, along with its binding protein, IGF binding protein 3, and acid-labile protein. Recombinant human (rh) IGF-I (mecasermin) is approved by the US FDA and the European Medicines Agency for the treatment of patients with severe primary IGF deficiency or for patients with GH1 gene deletion who have developed neutralizing antibodies to GH. It has been shown to increase growth velocity in children with either condition. In the past, there have been adverse events, particularly hypoglycemia, reported with the administration of mecasermin. However, a recent report of long-term therapy with mescasermin in children with severe IGF-I deficiency has concluded that although adverse events are common, they are rarely severe enough to interrupt or modify treatment. The serum half-life of mecasermin is shorter in patients with GH insensitivity syndrome and low serum levels of its binding protein, the insulin-like growth factor binding protein (IGFBP)-3 and acid-labile subunit, compared with the serum half-life in normal volunteers or in patients with an IGF1 gene deletion who have normal levels of IGFBP-3. Mecasermin rinfabate, a complex of rhIGF-I and rhIGFBP-3, appears to prolong the serum half-life and might counteract acute adverse events, particularly hypoglycemia, associated with the administration of mescasermin. Mecasermin rinfabate, however, is no longer available in the USA or Europe for treating conditions involving short stature, because of a legal requirement. Mecasermin has been shown to be effective in increasing height velocity and adult height in patients with severe GH resistance and in IGF1 gene deletion. There has been some interest in using mecasermin to treat patients with partial GH resistance or idiopathic short stature. At the present time, the data are insufficient to make this recommendation.

Recombinant human insulin-like growth factor-I therapy for children with growth disorders

Until recently, the only possible therapy available for treatment of children with significant short stature was recombinant human growth hormone (rhGH). However, recombinant human insulin-like growth factor-I (rhIGF-I) has now become commercially available as a therapeutic option to treat children of short stature caused by severe primary IGF-I deficiency, defined as: height standard deviation score (SDS) less than or equal to -3.0, basal IGF-I SDS less than or equal to -3.0, and normal or elevated levels of GH. Published data demonstrate that rhIGF-I therapy in patients with primary IGF-I deficiency accelerates growth significantly during the first year of treatment, but progressive attenuation is likely in subsequent years. The growth response to rhIGF-I is neither as intense nor as well sustained as the growth response to rhGH among children with GH deficiency. Despite increasing interest in the possibility for broader use of rhIGF-I for growth promotion, especially in children with idiopathic short stature (ISS), it is necessary to wait for studies assessing the efficacy and safety of rhIGF-I therapy in this condition. In this particular population (ISS patients), the combination of rhIGF-I and rhGH, compared with either hormone used alone, may have theoretical advantages. Hypoglycemia has been the most common side effect reported with use of rhIGF-I and is reasonably controlled with adequate food intake. Most of the other (long-term) adverse effects appear to be related to hyperstimulation of lymphoid tissue growth. Little is known about the long-term effects of IGF-I therapy in growing children, but caution and long-term, controlled, prospective trials of rhIGF-I-treated children and adolescents are needed.

Primary growth hormone (GH) insensitivity and insulin-like growth factor deficiency caused by novel compound heterozygous mutations of the GH receptor gene: genetic and functional studies of simple and compound heterozygous states

CONTEXT

Primary GH insensitivity (GHI) or Laron syndrome, caused by mutations of the GH receptor (GHR) gene, has a clinical phenotype of postnatal growth failure associated with normal elevated serum concentrations of GH and low serum levels of IGF-I.

OBJECTIVE

We investigated the clinical and biochemical implications of molecular defects in the GHR gene in an Austrian family with two daughters who were GHI.

PATIENTS

Patient 1 [height, -4.8 sd score (SDS)] and patient 2 (height, -5.0 SDS) had elevated circulating levels of GH, low-normal levels of GH-binding protein, and abnormally low IGF-I (-5.0 SDS and -2.6 SDS, respectively) and IGF-binding protein-3 (-2.6 SDS and -2.0 SDS, respectively).

RESULTS

Both patients carry novel compound, missense, heterozygous GHR mutations, C94S and H150Q. In vitro reconstitution experiments demonstrated that whereas each of the mutants could be stably expressed, GHR(C94S) lost its affinity for GH and could neither activate signal transducer and activator of transcription (STAT)-5b nor drive STAT5b-dependent gene transcription in response to GH (1-100 ng/ml). GHR(H150Q) showed normal affinity for GH but impaired capacity for signal transduction. The compound heterozygote and C94S heterozygote, but not the H150Q heterozygote, showed significant deficiency in activating GH-induced gene expression, corroborating diminished GH-induced STAT5b activation in fibroblasts carrying GHR(C94S) as either a compound heterozygote (in the patients) or a simple heterozygote (in one parent).

CONCLUSIONS

Each of the compound heterozygous mutations contributed additively to the pathological condition seen in the patients, and the more detrimental of the two mutations, C94S, may cause (partial) primary GHI, even in a heterozygous state.