Recombinant human growth hormone plus recombinant human insulin-like growth factor-1 coadministration therapy in short children with low insulin-like growth factor-1 and growth hormone sufficiency: results from a randomized, multicenter, open-label, parallel-group, active treatment-controlled trial

IGF1 Haploinsufficiency: Phenotype and Response to Growth Hormone Treatment in 9 Patients

INTRODUCTION

The clinical features of bi-allelic IGF1 defects are well established, i.e., severe growth failure and microcephaly, delayed psychomotor development, and sensorineural deafness. However, information on clinical and endocrine consequences of heterozygous IGF1 variants and treatment options is scarce. We aimed at extending the knowledge base of the clinical presentation and growth response to recombinant human growth hormone (rhGH) of patients carrying such variants.

METHODS

Retrospective case series of patients with pathogenic heterozygous IGF1 variants.

RESULTS

Nine patients from six families were included, harbouring five whole or partial gene deletions and one frameshift variant resulting in a premature stop codon (three de novo, one unknown inheritance). In the other two families, variants segregated with short stature. Mean (SD) birth length was -1.9 (1.3) SDS (n = 7), height -3.8 (0.6) SDS, head circumference -2.5 (0.6) SDS, serum IGF-I -1.9 (0.7) SDS, serum IGFBP-3 1.1 (0.4) SDS (n = 7), and GH peak range 5-31 μg/L (n = 4). Five patients showed feeding problems in infancy. Average height increased after 1 and 2 years of rhGH treatment by 0.8 SDS (range 0.3-1.3 SDS) and 1.3 SDS (range 0.5-2.0 SDS), respectively. Adult height in 2 patients was -2.8 and -1.3 SDS, which was, respectively, 1.3 and 2.9 SDS taller than predicted before start of treatment.

CONCLUSION

Haploinsufficiency of IGF1 causes a variable phenotype of prenatal and postnatal growth failure, microcephaly, feeding difficulties, low/low-normal serum IGF-I values in contrast to serum IGFBP-3 in the upper-normal range. Treatment with rhGH increased growth in the first 2 years of treatment, and in 2 patients adult height after treatment was higher than predicted at treatment initiation.

Combined growth hormone and insulin-like growth factor-1 rescues growth retardation in glucocorticoid-treated mdxmice but does not prevent osteopenia

Short stature and osteoporosis are common in Duchenne muscular dystrophy (DMD) and its pathophysiology may include an abnormality of the growth hormone/insulin-like growth factor-1 (GH/IGF-1) axis, which is further exacerbated by long-term glucocorticoid (GC) treatment. Hence, an agent that has anabolic properties and may improve linear growth would be beneficial in this setting and therefore requires further exploration. A 5-week-old x-linked muscular dystrophy (mdx) mice were used as a model of DMD. They were treated with prednisolone ± GH + IGF-1 for 4 weeks and then compared to control mdx mice to allow the study of both growth and skeletal structure. GC reduced cortical bone area, bone fraction, tissue area and volume and cortical bone volume, as assessed by micro computed tomography (CT) In addition, GC caused somatic and skeletal growth retardation but improved grip strength. The addition of GH + IGF-1 therapy rescued the somatic growth retardation and induced additional improvements in grip strength (16.9% increase, P < 0.05 compared to control). There was no improvement in bone microarchitecture (assessed by micro-CT and static histomorphometry) or biomechanical properties (assessed by three-point bending). Serum bone turnover markers (Serum procollagen 1 intact N-terminal propeptide (P1NP), alpha C-terminal telopeptide (αCTX)) also remained unaffected. Further work is needed to maximise these gains before proceeding to clinical trials in boys with DMD.

Identification and In Vitro Functional Verification of Two Novel Mutations of GHR Gene in the Chinese Children with Laron Syndrome

PURPOSE

Laron syndrome (LS) is a severe growth disorder caused by GHR gene mutation or post-receptor pathways defect. The clinical features of these patients collected in our present study were summarized, GHR gene variants were investigated and further in vitro functional verification was carried out.

METHODS

Four patients with LS were collected, their clinical characteristics were summarized, genomic DNA was extracted, and GHR gene was amplified and sequenced. GHR wild type (GHR-WT) and mutant GHR expression plasmids were constructed, and transiently transfected into HepG2 cells and HEK293T cells to observe the subcellular distribution of the GHR protein by immunofluorescence and to determine the expression of GHR and its post-receptor signaling pathway changes by Western blotting.

RESULTS

All of the four patients were male, and the median height was -4.72 SDS. Four GHR gene variants including c.587A>C (p.Y196S), c.766C>T (p.Q256*), c.808A>G (p.I270V) and c.1707-1710del (p.E570Afs*30) were identified, and the latter two were novel mutations. The results of mutant GHR plasmids transfection experiments and immunofluorescence assay showed that the subcellular distribution of GHR-Q256* and GHR-E570Afs*30 mutant proteins in HepG2 and HEK293T cells presented with a unique ring-like pattern, gathering around the nucleus, while GHR-Y196S mutant protein was evenly distributed on HepG2 cell membrane similar to GHR-WT. The GHR protein levels of HepG2 cells transiently transfected with GHR-Y196S, GHR-Q256* and GHR-E570Afs*30 were all significantly lower when compared with cells transfected with GHR-WT (P<0.05). Further mutant GHR post-receptor signal transduction investigation demonstrated that GH induced phosphorylated STAT5 levels of HepG2 cells transfected with three mutant plasmids were all significantly decreased in comparison with that of GHR-WT (P<0.05).

CONCLUSIONS

Two novel GHR gene mutations (I270V and E570Afs*30) were found in our patients with LS. GHR mutations influenced the subcellular distribution and GHR protein levels, then led to the impaired post-receptor signal transduction, suggesting that the GHR mutations contributed to the pathological condition of LS patients.

A rationale for the treatment of short stature in children with the combination of recombinant human growth hormone (rhGH) and recombinant human insulin-like growth factor-I (rhIGF-I)

Both rhGH and rhIGF-I are signaling molecules with the capacity to restore the rate of growth in certain subsets of slowly growing children. In some instances, heights attained at or near the time of cessation of linear growth are indistinguishable from the height distribution of the community as a whole or from the height distribution expected based on the heights of biological parents. The GH: IGF-I signaling system is sequential, forming a continuous loop wherein GH will stimulate production of IGF-I and IGF-I will inhibit production of GH. This feature suggests that a deficiency of GH will be accompanied by a deficiency of IGF-I and that treatment of GH deficiency with rhGH will restore IGF-I and the subnormal growth of combined GH: IGF-I deficiency. Although logical, this proposition is not always true. rhGH and rhIGF-I are distinct polypeptides, with distinct cell surface receptors and distinct intracellular signaling pathways both capable of amplifying distinct, yet overlapping, patterns of gene replication, protein synthesis and metabolic activities. These features suggest that neither treatment with rhGH nor rhIGF-I alone will invariably recapitulate the combined activities of the GH: IGF-I system, At the present time, this proposition appears both logical and true. The possibility that combined rhGH and rhIGF-I treatment can accomplish that which neither monotherapy can has been examined in gene knock-out experiments in animals and direct comparisons of GH, IGF-I and combined GH: IGF- treatments in animals and in children with short stature, normal GH and low IGF-I (primary IGF-I deficiency). In these experimental models, the growth rates with combined rhGH and rhIGF-I treatment exceed those of either monotherapy. The extent to which this proposition can be generalized to various short stature populations remains to be determined.

The Challenge of Defining and Investigating the Causes of Idiopathic Short Stature and Finding an Effective Therapy

Idiopathic short stature (ISS) comprises a wide range of conditions associated with short stature that elude the conventional diagnostic work-up and are often caused by still largely unknown genetic variants. In the last decade, the improvement of diagnostic techniques has led to the discovery of causal mutations in genes involved in the function of the growth hormone (GH)/insulin-like growth factor-I (IGF-I) axis as well as in growth plate physiology. However, many cases of ISS remain idiopathic. In the future, the more frequent identification of the underlying causes will allow a better stratification of subjects and offer a tailored management. GH therapy has been proposed and approved in some countries for the treatment of children with ISS. To improve the efficacy of GH therapy, trials with GH combined with GnRH agonists, aromatase inhibitors, and even IGF-I have been conducted. This review aims to revise the current definition of ISS and discuss the management of children with ISS on the basis of the most recent evidence.

Nonclassical GH Insensitivity: Characterization of Mild Abnormalities of GH Action

GH insensitivity (GHI) presents in childhood with growth failure and in its severe form is associated with extreme short stature and dysmorphic and metabolic abnormalities. In recent years, the clinical, biochemical, and genetic characteristics of GHI and other overlapping short stature syndromes have rapidly expanded. This can be attributed to advancing genetic techniques and a greater awareness of this group of disorders. We review this important spectrum of defects, which present with phenotypes at the milder end of the GHI continuum. We discuss their clinical, biochemical, and genetic characteristics. The objective of this review is to clarify the definition, identification, and investigation of this clinically relevant group of growth defects. We also review the therapeutic challenges of mild GHI.

Genetics of Growth Disorders-Which Patients Require Genetic Testing?

The second 360° European Meeting on Growth Hormone Disorders, held in Barcelona, Spain, in June 2017, included a session entitled Pragmatism vs. Curiosity in Genetic Diagnosis of Growth Disorders, which examined current concepts of genetics and growth in the clinical setting, in terms of both growth failure and overgrowth. For patients with short stature, multiple genes have been identified that result in GH deficiency, which may be isolated or associated with additional pituitary hormone deficiencies, or in growth hormone resistance, primary insulin-like growth factor (IGF) acid-labile subunit deficiency, IGF-I deficiency, IGF-II deficiency, IGF-I resistance, and primary PAPP-A2 deficiency. While genetic causes of short stature were previously thought to primarily be associated with the GH-IGF-I axis, it is now established that multiple genetic anomalies not associated with the GH-IGF-I axis can result in short stature. A number of genetic anomalies have also been shown to be associated with overgrowth, some of which involve the GH-IGF-I axis. In patients with overgrowth in combination with an intellectual disability, two predominant gene families, the epigenetic regulator genes, and PI3K/AKT pathway genes, have now been identified. Specific processes should be followed for decisions on which patients require genetic testing and which genes should be examined for anomalies. The decision to carry out genetic testing should be directed by the clinical process, not merely for research purposes. The intention of genetic testing should be to direct the clinical options for management of the growth disorder.

Genetic causes of proportionate short stature

Human growth is a very complex phenomenon influenced by genetic, hormonal, nutritional and environmental factors, from fetal life to puberty. Although the GH-IGF axis has a central role with specific actions on growth, numerous genes are involved in the control of stature. Genome-wide association studies have identified >600 variants associated with human height, still explaining only a small fraction of phenotypic variation. Since short stature in childhood is a common reason for referral, pediatric endocrinologists must be aware of the multifactorial and polygenic contributions to height. Multiple disorders characterized by growth failure of prenatal and/or postnatal onset due to single gene defects have been described. Their early diagnosis, facilitated by advances in genomic technologies, is of upmost importance for their clinical management and to provide genetic counseling. Here we review the current clinical and genetic information regarding different syndromes and hormone abnormalities with proportionate short stature as the main feature, and provide an update of the approach for diagnosis and management.

Novel Dominant-Negative GH Receptor Mutations Expands the Spectrum of GHI and IGF-I Deficiency

Context:

Autosomal-recessive mutations in the growth hormone receptor (GHR) are the most common causes for primary growth hormone insensitivity (GHI) syndrome with classical GHI phenotypically characterized by severe short stature and marked insulin-like growth factor (IGF)-I deficiency. We report three families with dominant-negative heterozygous mutations in the intracellular domain of the GHR causing a nonclassical GHI phenotype.

Objective:

To determine if the identified GHR heterozygous variants exert potential dominant-negative effects and are the cause for the GHI phenotype in our patients.

Results:

All three mutations (c.964dupG, c.920_921insTCTCAAAGATTACA, and c.945+2T>C) are predicted to result in frameshift and early protein termination. In vitro functional analysis of variants c.964dupG and c.920_921insTCTCAAAGATTACA (c.920_921ins14) suggests that these variants are expressed as truncated proteins and, when coexpressed with wild-type GHR, mimicking the heterozygous state in our patients, exert dominant-negative effects. Additionally, we provide evidence that a combination therapy of recombinant human growth hormone (rhGH) and rhIGF-I improved linear growth to within normal range for one of our previously reported patients with a characterized, dominant-negative GHR (c.899dupC) mutation.

Conclusion:

Dominant-negative GHR mutations are causal of the mild GHI with substantial growth failure observed in our patients. Heterozygous defects in the intracellular domain of GHR should, therefore, be considered in cases of idiopathic short stature and IGF-I deficiency. Combination therapy of rhGH and rhIGF-I improved growth in one of our patients.

Challenges in the Management of Short Stature

Human growth, from fetal life to adolescence, is dynamic and a good marker of health. Growth is a complex process influenced by genetic, hormonal, nutritional and environmental factors, both pre- and postnatally. To date, no international agreement regarding normal height has been established. Auxological parameters are fundamental to investigate potential short stature (SS), either with a known diagnosis, e.g. disproportionate or proportionate, prenatal and/or postnatal onset, or an unknown diagnosis, i.e. idiopathic SS. The incidence/prevalence of SS is difficult to establish. The measurement of choice in children aged <2 years is length, while in those >2 years of age it is height. A number of monogenic diseases that lead to proportionate SS due to either isolated growth hormone deficiency, multiple pituitary hormone deficiency, growth hormone insensitivity, primary acid-labile subunit deficiency, primary IGF-1 deficiency, IGF-1 resistance, primary IGF-2 deficiency or primary protease deficiency have been discovered in the last 30 years. In addition, the Nosology and Classification of Genetic Skeletal Disorders revised in 2015 includes 436 conditions, with a number of genes of 364. A practical algorithm for the evaluation of SS as well as therapeutic options are discussed.

The future of growth-promoting therapy

Growth hormone (GH) has been in use for 50 years in children with short stature. Recent developments suggest that our traditional approaches to growth-promoting therapy will be challenged in the following areas:1)Diagnostic: The diagnosis of GH deficiency has always been problematic, largely due to limitations inherent in GH stimulation tests and related biochemical measures. The development of new tools for diagnosis of genetic etiologies of hormonal deficiencies and insensitivity, as well as the growing availability of such methodologies, will greatly strengthen existing diagnostic strategies. 2)Therapeutic: Long-acting GH preparations are already in clinical trials. IGF-I therapy is approved for treatment of IGF deficiency. Novel approaches to select skeletal dysplasias show promise and will potentially expand our therapeutic armamentarium. 3) Monitoring: Traditional weight-based dosing of GH will be supplemented by IGF-based and auxology-based strategies, allowing greater individualization of therapy. 4) Safety: Growth-promoting therapies will continue to require careful monitoring of safety. Recent consensus workshops have advocated life-time surveillance programs. 5) Ethics: Questions will continue to be raised concerning ethical issues related to growth-promoting therapy in children. The availability of new tools for diagnosis and monitoring will address some, but not all, of these issues.