Diagnostic and therapeutic advances in growth hormone insensitivity

Short stature related to Growth Hormone Insensitivity (GHI) in childhood

Linear growth during childhood is the result of the synergic contribution of different factors. The best growth determinant system during each period of life is represented by the growth hormone-insulin-like growth factor axis (GH-IGF), even if several other factors are involved in normal growth. Within the broad spectrum of growth disorders, an increased importance has been placed on growth hormone insensitivity (GHI). GHI was reported for the first time by Laron as a syndrome characterized by short stature due to GH receptor (GHR) mutation. To date, it is recognized that GHI represents a wide diagnostic category, including a broad spectrum of defects. The peculiar characteristic of GHI is the low IGF-1 levels associated with normal or elevated GH levels and the lack of IGF-1 response after GH administration. Recombinant IGF-1 preparations may be used in the treatment of these patients.

Severe growth failure associated with a novel heterozygous nonsense mutation in the GHR transmembrane domain leading to elevated growth hormone binding protein

OBJECTIVE

To report a novel mutation in GHR and to characterize a novel mechanism of nonclassical growth hormone insensitivity.

CONTEXT

Laron syndrome (LS) is a well-described disorder of growth hormone insensitivity due to mutations in the growth hormone receptor (GHR) that leads to short stature. Biochemically, LS patients classically have elevated levels of growth hormone (GH), but low levels of insulin-like growth factor (IGF)-1, IGF binding protein (IGFBP)-3 and GH binding protein (GHBP).

DESIGN

Case presentation with in vitro functional studies.

PATIENTS

A young male Caucasian child with short stature was found to have growth hormone insensitivity manifested by elevated levels of GH and GHBP.

MEASUREMENTS

Growth hormone stimulation tests revealed baseline GH level of 20.9 µg/L and maximum stimulated GH level of 52.7 µg/L and GHBP level of 4868 pmol/L. GHR gene sequencing revealed a novel heterozygous nonsense mutation (c.800G > A, p.Trp267*) in the transmembrane domain of the receptor. Immunoblot analysis of transfected GHR p.Trp267* in HEK293 revealed inhibition of GH-induced STAT5 signalling that was overcome with increasing doses of recombinant human GH.

RESULTS

Using an in vitro model, we show that elevated levels of GHBP inhibit the action of GH. Furthermore, our studies demonstrate that this inhibition by GHBP can be overcome by increasing doses of recombinant human GH.

CONCLUSIONS

To our knowledge, this is the first study to demonstrate in vitro that elevated levels of GHBP attenuate the effect of GH and inhibit GH-induced signalling, thereby leading to short stature. Though this inhibition was overcome in vitro with supraphysiologic doses of GH, significantly above endogenously available GH, it remains to be seen whether such an effect can be replicated in vivo.

Growth hormone insensitivity: diagnostic and therapeutic approaches

INTRODUCTION

Growth hormone resistance defines several genetic (primary) and acquired (secondary) pathologies that result in completely or partially interrupted activity of growth hormone. An archetypal disease of this group is the Laron-type dwarfism caused by mutations in growth hormone receptors. The diagnosis is based on high basal levels of growth hormone, low insulin like growth factor-I (IGF-1) level, unresponsiveness to IGF generation test and genetic testing. Recombinant IGF-1 preparations are used in the treatment

CONCLUSION

In this article, clinical characteristics, diagnosis and therapeutic approaches of the genetic and other diseases leading to growth hormone insensitivity are reviewed.

Further observations on the effects of long-term treatment with recombinant human insulin-like growth factor 1 in growth hormone insensitivity syndrome

BACKGROUND/AIM

Growth hormone insensitivity syndrome (GHIS) is a spectrum of disorders. Laron syndrome was the earliest discovered. Insulin-like growth factor 1 (IGF-1) therapy is used to improve growth. IGF-1 has diverse effects on the growth of body organs. We aim to assess the long-term effects of IGF-1 therapy in patients with GHIS particularly on adiposity and acral growth.

METHODS

Six patients (5 with Laron syndrome and 1 with type 1A growth hormone deficiency) were followed for a mean (±SD) of 8.2 ± 1.8 years. Mean age at start of therapy was 7.6 ± 4.1 years. Anthropometric evaluation including growth of hand, foot, ear, and skin folds, and assessment of internal organ growth were done.

RESULTS

Hand and foot sizes improved significantly, especially when treatment was initiated early. Prominent effects on adiposity were observed, reflected by increment in body mass index standard deviation score (SDS) and skin fold SDS. Mean height, height velocity, sitting height, and head circumference SDS improved with therapy. A significant increase in spleen and right kidney was appreciated.

CONCLUSION

IGF-1 therapy improves growth in GHIS. The hand and foot sizes increase significantly with therapy, and can even normalize with early initiation of treatment. Ear length further improves with therapy. Other effects include increase in adiposity and internal organ growth.

Repair of aberrant splicing in growth hormone receptor by antisense oligonucleotides targeting the splice sites of a pseudoexon

CONTEXT

The GH receptor (GHR) pseudoexon 6Psi defect is a frequent cause of GH insensitivity (GHI) resulting from a non-functioning GH receptor (GHR). It results in a broad range of phenotypes and may also be present in patients diagnosed as idiopathic short stature.

OBJECTIVE

Our objective was to correct aberrant GHR splicing and inclusion of 6Psi using exon-skipping antisense oligonucleotides (ASOs).

DESIGN AND SETTING

Three ASOs binding the 5' (ASO-5), 3' (ASO-3), and branch site (ASO-Br) of 6Psi were tested in an in vitro splicing assay and a cell transfection system. The wild-type (wt) and mutant (mt) DNA minigenes (wt- and mtL1-GHR6Psi-L2, respectively) were created by inserting the GHR 6Psi in a well-characterized splice reporter (Adml-par). For the in vitro splicing assay, the wt- and mtL1-GHR6Psi-L2 were transcribed into pre-mRNA in the presence of [alpha(32)P]GTP and incubated with ASOs in HeLa nuclear extracts. For the cell transfection studies, wt- and mtL1-GHR6Psi-L2 cloned into pcDNA 3.1 were transfected with ASOs into HEK293 cells. After 48 h, RNA was extracted and radiolabeled RT-PCR products quantified.

RESULTS

ASO-3 induced an almost complete pseudoexon skipping in vitro and in HEK293 cells. This effect was dose dependent and maximal at 125-250 nm. ASO-5 produced modest pseudoexon skipping, whereas ASO-Br had no effect. Targeting of two splice elements simultaneously was less effective than targeting one. ASO-Br was tested on the wtL1-GHR6Psi-L2 and did not act as an enhancer of 6Psi inclusion.

CONCLUSIONS

The exon-skipping ASO approach was effective in correcting aberrant GHR splicing and may be a promising therapeutic tool.

Acid-labile subunit deficiency and growth failure: description of two novel cases

BACKGROUND/AIMS

Mutations in the acid-labile subunit (ALS) gene (IGFALS) have been associated with circulating insulin-like growth factor I (IGF-I) deficiency and short stature. Whether severe pubertal delay is also part of the phenotype remains controversial due to the small number of cases reported. We report 2 children with a history of growth failure due to novel IGFALS mutations.

METHODS

The growth hormone receptor gene (GHR) and IGFALS were analyzed by direct sequencing. Ternary complex formation was studied by size exclusion chromatography.

RESULTS

Two boys of 13.3 and 10.6 years, with pubertal stages 2 and 1, had mild short stature (-3.2 and -2.8 SDS, respectively) and a biochemical profile suggestive of growth hormone resistance. No defects were identified in the GHR. Patient 1 was homozygous for the IGFALS missense mutation P73L. Patient 2 was a compound heterozygote for the missense mutation L134Q and a novel GGC to AG substitution at position 546-548 (546-548delGGCinsAG). The latter causes a frameshift and the appearance of a premature stop codon. Size exclusion chromatography showed no peaks corresponding to ternary and binary complexes in either patient.

CONCLUSION

Screening of the IGFALS is important in children with short stature associated with low serum IGF-I, IGFBP-3 and ALS.

Identification and characterisation of a novel GHR defect disrupting the polypyrimidine tract and resulting in GH insensitivity

OBJECTIVE

GH insensitivity (GHI) is caused in the majority of cases by impaired function of the GH receptor (GHR). All but one known GHR mutation are in the coding sequence or the exon/intron boundaries. We identified and characterised the first intronic defect occurring in the polypyrimidine tract of the GHR in a patient with severe GHI.

DESIGN

We investigated the effect of the novel defect on mRNA splicing using an in vitro splicing assay and a cell transfection system.

METHODS

GHR was analysed by direct sequencing. To assess the effect of the novel defect, two heterologous minigenes (wild-type and mutant L1-GHR8-L2) were generated by inserting GHR exon 8 and its flanking wild-type or mutant intronic sequences into a well-characterised splicing reporter (Adml-par L1-L2). (32)P-labelled pre-mRNA was generated from the two constructs and incubated in HeLa nuclear extracts or HEK293 cells.

RESULTS

Sequencing of the GHR revealed a novel homozygous defect in the polypyrimidine tract of intron 7 (IVS7-6T>A). This base change does not involve the highly conserved splice site sequences, and is not predicted in silico to affect GHR mRNA splicing. Nevertheless, skipping of exon 8 from the mutant L1-GHR8-L2 mRNA was clearly demonstrated in the in vitro splicing assay and in transfected HEK293 cells.

CONCLUSION

Disruption of the GHR polypyrimidine tract causes aberrant mRNA splicing leading to a mutant GHR protein. This is predicted to lack its transmembrane and intracellular domains and, thus, be incapable of transducing a GH signal.

Dental Development in Children with Growth Hormone Insensitivity Syndrome: Demirjian Analysis of Serial Panoramic Radiographs

Objective:

This study evaluates the effects of 8 years of insulinlike growth factor-I therapy on tooth development in patients with growth hormone insensitivity syndrome.

Methods:

Forty-nine panoramic radiographs were evaluated from eight patients (six boys, two girls). Seven teeth in the mandibular left region were graded according to the Demirjian system. Radiographs were taken at the start of insulinlike growth factor-I therapy and were continued at approximately yearly intervals for 8 years.

Results:

Three of six boys and one of two girls who began treatment with insulinlike growth factor-I at earlier ages experienced an increase in the rate of tooth development. One of six boys who began treatment with insulinlike growth factor-I at a later age had a slower rate of dental development. The patients had more rapid tooth maturation during the beginning of treatment. By the end of treatment, all patients had normal dental maturity for their age.

Conclusions:

Treatment of growth hormone insensitivity syndrome with insulinlike growth factor-I appears to lead to an increase in dental maturation, particularly in younger patients. After 8 years all patients had achieved normal dental development.

An intronic growth hormone receptor mutation causing activation of a pseudoexon is associated with a broad spectrum of growth hormone insensitivity phenotypes

CONTEXT

Inherited GH insensitivity (GHI) is usually caused by mutations in the GH receptor (GHR). Patients present with short stature associated with high GH and low IGF-I levels and may have midfacial hypoplasia (typical Laron syndrome facial features). We previously described four mildly affected GHI patients with an intronic mutation in the GHR gene (A(-1)-->G(-1) substitution in intron 6), resulting in the activation of a pseudoexon (6Psi) and inclusion of 36 amino acids.

OBJECTIVE

The study aimed to analyze the clinical and genetic characteristics of additional GHI patients with the pseudoexon (6Psi) mutation.

DESIGN/PATIENTS

Auxological, biochemical, genetic, and haplotype data from seven patients with severe short stature and biochemical evidence of GHI were assessed.

MAIN OUTCOME MEASURES

We assessed genotype-phenotype relationship.

RESULTS

One patient belongs to the same extended family, previously reported. She has normal facial features, and her IGF-I levels are in the low-normal range for age. The six unrelated patients, four of whom have typical Laron syndrome facial features, have heights ranging from -3.3 to -6.0 sd and IGF-I levels that vary from normal to undetectable. We hypothesize that the marked difference in biochemical and clinical phenotypes might be caused by variations in the splicing efficiency of the pseudoexon.

CONCLUSIONS

Activation of the pseudoexon in the GHR gene can lead to a variety of GHI phenotypes. Therefore, screening for the presence of this mutation should be performed in all GHI patients without mutations in the coding exons.

Final Height in Patients with Idiopathic Short Stature and High Growth Hormone Responses to Stimulation Tests

Children with idiopathic short stature (ISS) may have normal or increased growth hormone (GH) responses to provocation tests and achieve a final height (FH) below -2.0 standard deviation score (SDS) if untreated. FH of subjects with high stimulated GH levels has not been studied in detail.

AIM

It was the aim of this study to analyse FH in ISS patients with high GH peak responses to the provocation test.

PATIENTS AND METHODS

We studied 16 patients (9 pre-pubertal) with ISS and a GH peak >or=40 mU/l to insulin-induced hypoglycaemia. The patients were recalled at age 19.7 +/- 2.5 years for measurement of FH when blood samples were obtained for serum insulin-like growth factor (IGF)-I, IGF binding protein 3, acid-labile subunit and GH binding protein measurements. GH bioactivity was determined using the Nb2 bioassay.

RESULTS

FH was -3.1 +/- 1.0 SDS, being significantly lower than target height (TH). At FH, IGF-I levels were within -1.5 and +1.5 SDS for age and sex in 10 patients and higher than +1.5 SDS in 6 patients. IGF binding protein 3, acid-labile subunit, GH binding protein levels and GH bioactivity values were normal.

SUMMARY

These data suggest that patients with ISS and high GH levels during a GH stimulation test may have a more compromised FH. The association of severe ISS with a peak GH >40 mU/l might suggest a degree of insensitivity for the GH-IGF-I axis.

Endocrine assessment, molecular characterization and treatment of growth hormone insensitivity disorders

Advances in the diagnosis and treatment of growth hormone insensitivity disorders have occurred in the past 15 years. We discuss the current status of endocrine and molecular evaluation, focusing on the pediatric age range. All the identified mutations of the growth hormone receptor are included. Treatment with recombinant human insulin-like growth factor (rhIGF) 1 in classical cases is summarized and new targets for treatment are discussed, together with therapy using the complex formed between rhIGF1 and rhIGF-binding protein 3.