Standard and low-dose IGF-I generation tests and spontaneous growth hormone secretion in children with idiopathic short stature

Differential Diagnosis of the Short IGF-I-Deficient Child with Apparently Normal Growth Hormone Secretion

The current differential diagnosis for a short child with low insulin-like growth factor I (IGF-I) and a normal growth hormone (GH) peak in a GH stimulation test (GHST), after exclusion of acquired causes, includes the following disorders: (1) a decreased spontaneous GH secretion in contrast to a normal stimulated GH peak ("GH neurosecretory dysfunction," GHND) and (2) genetic conditions with a normal GH sensitivity (e.g., pathogenic variants of GH1 or GHSR) and (3) GH insensitivity (GHI). We present a critical appraisal of the concept of GHND and the role of 12- or 24-h GH profiles in the selection of children for GH treatment. The mean 24-h GH concentration in healthy children overlaps with that in those with GH deficiency, indicating that the previously proposed cutoff limit (3.0-3.2 μg/L) is too high. The main advantage of performing a GH profile is that it prevents about 20% of false-positive test results of the GHST, while it also detects a low spontaneous GH secretion in children who would be considered GH sufficient based on a stimulation test. However, due to a considerable burden for patients and the health budget, GH profiles are only used in few centres. Regarding genetic causes, there is good evidence of the existence of Kowarski syndrome (due to GH1 variants) but less on the role of GHSR variants. Several genetic causes of (partial) GHI are known (GHR, STAT5B, STAT3, IGF1, IGFALS defects, and Noonan and 3M syndromes), some responding positively to GH therapy. In the final section, we speculate on hypothetical causes.

GH Responsiveness in Children With Noonan Syndrome Compared to Turner Syndrome

BACKGROUND

Despite different genetic background, Noonan syndrome (NS) shares similar phenotype features to Turner syndrome (TS) such as short stature, webbed neck and congenital heart defects. TS is an entity with decreased growth hormone (GH) responsiveness. Whether this is found in NS is debated.

METHODS

Data were retrieved from combined intervention studies including 25 children diagnosed with NS, 40 diagnosed with TS, and 45 control children (all prepubertal). NS-children and TS-girls were rhGH treated after investigation of the GH/IGFI-axis. GH was measured with poly- and monoclonal antibodies; 24hGH-profile pattern analysed by PULSAR. The NS-children were randomly assigned to Norditropin^® 33 or 66 μg/kg/day, and TS-girls were consecutively treated with Genotropin^® 33 or 66 μg/kg/day.

RESULTS

Higher PULSAR-estimates of 24h-profiles were found in both NS-children and TS-girls compared to controls: Polyclonal GH_max24h-profile (Mean ± SD) was higher in both groups (44 ± 23mU/L, p<0.01 in NS; 51 ± 47, p<0.001 in TS; compared to 30 ± 23 mU/L in controls) as was GH-baseline (1.4 ± 0.6 mU/L in NS; 2.4 ± 2.4 mU/L in TS, p<0.01 for both, compared to 1.1 ± 1.2 mU/L in controls). Pre-treatment IGFI_SDS was 2.2 lower in NS-children (-1.7 ± 1.3) compared to TS-girls (0.6 ± 1.8, p<0.0001). GH_max, IGFI/IGFBP3-ratio_SDS, and chronological age at start of GH accounted for 59% of the variance in first-year growth response in NS.

CONCLUSION

Both prepubertal NS-children and TS-girls had a high GH secretion, but low IGFI/IGFBP3 levels only in NS-children. Both groups presented a broad individual response. NS-children showed higher response in IGFI and growth, pointing to higher responsiveness to GH treatment than TS-girls.

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.

Towards a Rational and Efficient Diagnostic Approach in Children Referred for Growth Failure to the General Paediatrician

Based on a recent Dutch national guideline, we propose a structured stepwise diagnostic approach for children with growth failure (short stature and/or growth faltering), aiming at high sensitivity for pathologic causes at acceptable specificity. The first step is a detailed clinical assessment, aiming at obtaining relevant clinical clues from the medical history (including family history), physical examination (emphasising head circumference, body proportions and dysmorphic features) and assessment of the growth curve. The second step consists of screening: a radiograph of the hand and wrist (for bone age and assessment of anatomical abnormalities suggestive for a skeletal dysplasia) and laboratory tests aiming at detecting disorders that can present as isolated short stature (anaemia, growth hormone deficiency, hypothyroidism, coeliac disease, renal failure, metabolic bone diseases, renal tubular acidosis, inflammatory bowel disease, Turner syndrome [TS]). We advise molecular array analysis rather than conventional karyotyping for short girls because this detects not only TS but also copy number variants and uniparental isodisomy, increasing diagnostic yield at a lower cost. Third, in case of diagnostic clues for primary growth disorders, further specific testing for candidate genes or a hypothesis-free approach is indicated; suspicion of a secondary growth disorder warrants adequate further targeted testing.

Idiopathic short stature and growth hormone sensitivity in prepubertal children

OBJECTIVE

We compared growth hormone sensitivity to an insulin-like growth factor I (IGF-I) generation test in children with idiopathic short stature (ISS) and of normal stature (NS) across the birthweight range.

METHODS

Forty-six prepubertal children (~7.1 years) born at term were studied: ISS (n = 23; 74% boys) and NS (n = 23; 57% boys). Children underwent a modified IGF-I generation test with recombinant human growth hormone (rhGH; 0.05 mg/kg/d) over four consecutive days. Hormonal concentrations were measured at baseline and day 5.

RESULTS

Children with idiopathic short stature were 1.90 SDS lighter (P < 0.0001) but had 4.5% more body fat (P = 0.0007) than NS children. Overall, decreasing birthweight SDS across the normal range (-1.9 to +1.5 SDS) was associated with lower percentage IGF-I response to rhGH stimulation in univariable (r = 0.45; P = 0.002) and multivariable models (β = 24.6; P = 0.006). Plasma IGF-I concentrations rose in both groups with rhGH stimulation (P < 0.0001). GHBP levels (P = 0.002) were suppressed in ISS children (-19%; P = 0.029) but increased among NS children (+18%; P = 0.028), with contrasting responses also observed for leptin and IGFBP-1. Further, the increase in insulin concentrations in response to rhGH stimulation was ~3-fold greater in NS children (142% vs 50%; P = 0.006).

CONCLUSIONS

A progressive decrease in birthweight SDS was associated with a reduction in GH sensitivity in both NS and ISS children. Thus, the lower IGF-I response to rhGH stimulation in association with decreasing birthweight indicates that the ISS children at the lower end of the birthweight spectrum may have partial GH resistance, which may contribute to their poorer growth.

Etiology of short stature in Indian children and an assessment of the growth hormone-insulin-like growth factor axis in children with idiopathic short stature

Background Our objectives were to evaluate the etiology of short stature, assess the prevalence of idiopathic short stature (ISS) and assess the growth hormone (GH)-insulin-like growth factor (IGF) axis in children with ISS. Methods A stepwise diagnostic evaluation was done in 394 children aged 4-16 years with short stature. Children with no definitive etiology were labeled as ISS. In these children, baseline IGF-1, IGF binding protein-3 (IGFBP-3) and stimulated IGF-1 after administration of GH for 4 days were measured. Results Hypothyroidism (in 18.1%) and ISS (in 15.5%) were the commonest causes of short stature. In children with ISS (n=61), the mean baseline and stimulated IGF-1 standard deviation scores (SDSs) were -1.2±1.0 and -0.3±1.4, respectively, with levels below -2 SDS in 13 (21%) and six (10%) children, respectively. In 33 (54%) of the ISS patients, response to GH was suboptimal (increment in the IGF-1 level <40%). There was no difference in the mean peak GH, IGFBP-3 and baseline and stimulated IGF-1 levels between children with familial and non-familial ISS. A significant positive correlation of height SDS with baseline IGF-1 SDS (r=0.28, p=0.026), stimulated IGF-1 SDS (r=0.32, p=0.010) and ΔIGF-1 SDS (r=0.26, p=0.036) was observed in children with ISS. Conclusions Hypothyroidism and ISS were the commonest etiologies for short stature. The baseline IGF-1 was below -2 SDS in 21% and the increment after GH stimulation was suboptimal in 54% of children, indicating that a substantial proportion of children with ISS had an impaired GH-IGF axis.

A genetic approach to evaluation of short stature of undetermined cause

Short stature is a common presentation to paediatric endocrinologists. After exclusion of major endocrine or systemic disease, most children with short stature are diagnosed based on a description of their growth pattern and the height of their parents (eg, familial short stature). Height is a polygenic trait and genome-wide association studies have identified many of the associated genetic loci. Here we review the application of genetic studies, including copy number variant analysis, targeted gene panels, and whole-exome sequencing in children with idiopathic short stature. We estimate 25-40% of children diagnosed with idiopathic short stature could receive a molecular diagnosis using these technologies. A molecular diagnosis for short stature is important for affected individuals and their families and might inform treatment decisions surrounding use of growth hormone or insulin-like growth factor 1 therapy.

The growth hormone-insulin-like growth factor-I axis in the diagnosis and treatment of growth disorders

The growth hormone (GH)-insulin-like growth factor (IGF)-I axis is a key endocrine mechanism regulating linear growth in children. While paediatricians have a good knowledge of GH secretion and assessment, understanding and use of measurements of the components of the IGF system are less current in clinical practice. The physiological function of this axis is to increase the anabolic cellular processes of protein synthesis and mitosis, and reduction of apoptosis, with each being regulated in the appropriate target tissue. Measurement of serum IGF-I and IGF-binding protein (IGFBP)-3 concentrations can complement assessment of GH status in the investigation of short stature and contribute to prediction of growth response during GH therapy. IGF-I monitoring during GH therapy also informs the clinician about adherence and provides a safety reference to avoid over-dosing during long-term management.

Compound heterozygosity for two GHR missense mutations in a patient affected by Laron Syndrome: a case report

Background

Mutations localized in the Growth Hormone Receptor (GHR) gene are often associated with the pathogenesis of Laron Syndrome, an autosomal recessive hereditary disorder characterized by severe growth retardation. Biochemically, patients present normal to high circulating GH levels, in presence of very low or undetectable IGF-I levels, which do not rise after rhGH treatment.

Case presentation

We describe the case of a 3.8 years old girl with symmetrical short stature (−3.76 SDS), low IGF-1 and IGFBP-3, in presence of normal GH levels. Parents were not relatives and there was no family history of short stature. During the second day of birth, she developed severe hypoglycaemia that required glucose infusion. She presented frontal bossing and depressed nasal bridge. IGF-1 generation test showed no response, suggesting a GH resistance evidence. In the hypothesis of Laron Syndrome, we decided to perform a molecular analysis of Growth Hormone Receptor (GHR) gene. This analysis demonstrated that the patient was compound heterozygote for two missense mutations.

Conclusions

GHR gene mutations are a well demonstrated cause of GH insensitivity. In heterozygous patients, probably the normal stature may be achieved by a compensatory mechanism of GH secretion or signalling. On the contrary, in homozygous or compound heterozygous patients these compensatory mechanisms are inadequate, and short stature may be the consequence.

Growth hormone prescribing and initial BMI SDS: Increased biochemical adverse effects and costs in obese children without additional gain in height

Background

Recombinant human growth hormone (rhGH) treatment in children is usually prescribed using actual body weight. This may result in inappropriately high doses in obese children.

Methods

Retrospective audit of all paediatric patients treated with rhGH 2010–14 at a tertiary paediatric hospital in the UK. Change in height SDS and IGF-I SDS during the first year of treatment was stratified by initial BMI SDS in a mixed cohort, and a subgroup of GH deficient (GHD) patients. Alternative doses for those BMI SDS ≥2.0 (Obese) were calculated using BSA, IBW and LBW.

Results

354 patients (133 female) received rhGH, including 213 (60.2%) with GHD. Obesity was present in 40 patients (11.3%) of the unselected cohort, and 32 (15.0%) of the GHD cohort. For GHD patients, gain in height SDS was directly related to BMI SDS, except in obese patients (p<0.05). For both the entire cohort, and GHD patients only, IGF-1 SDS was significantly higher in obese patients (p<0.0001 for both groups). Cross sectional data identified 265 children receiving rhGH, 81 (30.5%) with a BMI-SDS ≥1.75. Alternate prescribing strategies for rhGH prescribing in obese patients suggest a saving of 27% - 38% annually.

Conclusions

Gain in IGF-I SDS is greater in obese children, and is likely to be related to relatively higher doses of rhGH. Additional gain in height was not achieved at the higher doses administered to obese children. Alternative dosing strategies in the obese patient population should be examined in rigorous clinical trials.

Insulin-like growth factor- I and factors affecting it in thalassemia major

Despite improvement of blood transfusion regimens and iron chelation therapy growth and maturational delay, cardiomyopathy, endocrinopathies and osteoporosis still occur in good number of thalassemic patients. Decreased IGF-1 secretion occurs in the majority of the thalassemic patients particularly those with growth and pubertal delay. Many factors contribute to this decreased synthesis of IGF-I including disturbed growth hormone (GH) - insulin-like growth factor - I (IGF-I) axis. The possible factors contributing to low IGF-I synthesis in thalassemia and the possible interaction between low IGF-I secretion and the occurrence of these complications is discussed in this mini-review. Improvement of IGF-I secretion in thalassemic patients should be intended to improve linear growth and bone mineral accretion in thalassemic patients. This can be attained through adequate correction of anemia and proper chelation, nutritional supplementation (increasing caloric intake), correction of vitamin D and zinc deficiencies, induction of puberty and correction of hypogonadism at the proper time and treating GH deficiency. This review paper provides a summary of the current state of knowledge regarding IGF-I and factors affecting it in patients with thalassaemia major (TM). Search on PubMed and reference lists of articles with the term 'IGF-I, GH, growth, thalassemia, thyroxine, anemia, vitamin D, and zinc' was carried out. A hundred and forty-eight articles were found and used in the write up and the data analyzed was included in this report.

IGF-1 and growth response to adult height in a randomized GH treatment trial in short non-GH-deficient children

CONTEXT

GH treatment significantly increased adult height (AH) in a dose-dependent manner in short non-GH-deficient children in a randomized, controlled, clinical trial; the mean gain in height SD score (heightSDS) was 1.3 (range 0-3), compared with 0.2 in the untreated group.

OBJECTIVE

The objective of the study was to analyze the relationship between IGF-1SDS, IGF binding protein-3 SDS (IGFBP3SDS), and their ratioSDS with a gain in the heightSDS until AH in non-GH-deficient short children.

DESIGN AND SETTING

This was a randomized, controlled, multicenter clinical trial.

INTERVENTION

The intervention included GH treatment: 33 or 67 μg/kg · d plus untreated controls.

SUBJECTS

One hundred fifty-one non-GH-deficient short children were included in the intent-to-treat (ITT) population and 108 in the per-protocol (PP) population; 112 children in the ITT and 68 children in the PP populations had idiopathic short stature (ISS).

MAIN OUTCOME MEASURES

Increments from baseline to on-treatment study mean IGF-1SDS (ΔIGF-1SDS), IGFBP3SDS, and IGF-1 to IGFBP3 ratioSDS were assessed in relationship to the gain in heightSDS.

RESULTS

Sixty-two percent of the variance in the gain in heightSDS in children on GH treatment could be explained by four variables: ΔIGF-1SDS (explaining 28%), bone age delay, birth length (the taller the better), and GH dose (the higher the better). The lower IGF-1SDS was at baseline, the higher was its increment during treatment. For both the AllPP- and the ISSPP-treated groups, the attained IGF-1SDS study level did not correlate with height gain.

CONCLUSION

In short non-GH-deficient children, the GH dose-related increment in IGF-1SDS from baseline to mean study level was the most important explanatory variable for long-term growth response from the peripubertal period until AH, when IGF-1SDS, IGFBP3SDS, and their ratioSDS were compared concurrently.

The systemic effects of platelet-rich plasma injection

BACKGROUND

Platelet-rich plasma (PRP) is an autologous blood product used to treat acute and chronic tendon, ligament, and muscle injuries in over 86,000 athletes in the United States annually. The World Anti-Doping Agency (WADA) banned intramuscular PRP injections in competitive athletes in 2010 because of concerns that it may increase performance-enhancing growth factors. The ban on PRP was removed in 2011 because of limited evidence for a systemic ergogenic effect of PRP, but the growth factors within PRP remain prohibited.

PURPOSE

To quantify the effect of PRP injection on systemic growth factors with performance-enhancing effects and to identify molecular markers to detect treated athletes.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Six ergogenic growth factors monitored by WADA-human growth hormone (hGH), insulin-like growth factor-1 (IGF-1), insulin-like growth factor binding protein-3 (IGFBP-3), basic fibroblast growth factor (bFGF or FGF-2), vascular endothelial growth factor (VEGF), and platelet-derived growth factor-BB (PDGF-BB)-were measured in 25 patients before (baseline) and at 0.25, 3, 24, 48, 72, and 96 hours after intratendinous leukocyte-rich PRP injection. Eating and exercise were prohibited for 3 hours before testing. Growth factors were quantified by enzyme-linked immunosorbent assay, and the change relative to each patient's baseline was calculated.

RESULTS

Relative to serum, PRP contained significantly more bFGF (226 vs 5 pg/mL), VEGF (1426 vs 236 pg/mL), and PDGF-BB (26,285 vs 392 pg/mL), but IGF-1 and hGH were not elevated. Serum levels increased significantly for IGF-1 at 24 and 48 hours, for bFGF at 72 and 96 hours, and for VEGF at 3, 24, 48, 72, and 96 hours after PRP injection. Additionally, VEGF was increased in all 25 patients after PRP treatment.

CONCLUSION

Serum IGF-1, VEGF, and bFGF levels are significantly elevated after PRP injection, supporting a possible ergogenic effect of PRP. An indirect marker for hGH doping, the product of IGFBP-3 × IGF-1, also significantly increased after PRP. Platelet-rich plasma appears to trigger an increase in circulating growth factors through activating biological pathways rather than by serving as a vehicle for the direct delivery of presynthesized growth factors. Elevated VEGF was observed in all patients after PRP, and ≥88% of patients had elevated VEGF at each time point from 3 to 96 hours after PRP, suggesting that VEGF may be a sensitive molecular marker to detect athletes recently treated with PRP.

CLINICAL RELEVANCE

This is the first and only adequately powered study of the systemic effects of PRP. We present evidence that PRP contains and may trigger systemic increases in substances currently banned in competitive athletes. Finally, we provide evidence that VEGF could serve as a useful molecular marker to detect athletes treated with PRP.

Diagnosis of endocrine disease: limitations of the IGF1 generation test in children with short stature

The IGF1 generation test (IGFGT) is often used during the assessment of suspected GH insensitivity (GHI). We report the results of a survey undertaken in 2010 to determine the use of IGFGT amongst members of the European Society for Paediatric Endocrinology to evaluate suspected GHI. The literature surrounding the usefulness and limitations of IGFGT are reviewed, and recommendations provided for its use. Of 112 paediatric endocrinologists from 30 countries who responded to the survey, 91 (81%) reported that they had used the IGFGT in the previous 2 years; >10 IGFGT protocols were used. The IGFGT impacted treatment decisions for 97% of the respondents and was a prerequisite for recombinant human IGF1 treatment for 45% of respondents. From a literature review, sensitivity of the IGFGT was evaluated as 77-91% in molecularly proven cases of GHI; specificity was ≤97%, depending on the protocol. The positive predictive value of the IGFGT is likely to be low, as the frequency of normality is predictably higher than that of abnormality in GH signalling. Given the limitations of the IGFGT in the most severe cases of GHI syndrome (GHIS), the ability of the IGFGT to detect less severe GHIS is doubtful. In a pragmatic approach, the IGFGT may not be useful for the diagnosis of GHIS.

Quantifying the risk of hypoglycaemia in children undergoing the glucagon stimulation test

OBJECTIVE

The low-dose (15-30 μg/kg) glucagon stimulation test (GST) is assumed to be associated with fewer episodes of low blood glucose (BG). We aimed to quantify the risk of hypoglycaemia in children undergoing the low-dose GST to evaluate their growth hormone status.

DESIGN AND PATIENTS

Blood glucose fluctuations during the GST in 80 children (median age 8·7 years, 45 boys, 66 prepubertal) who received a median 20·5 μg/kg of intramuscular glucagon were reviewed.

MEASUREMENTS

The rate of (i) hypoglycaemia (BG < 3·3 mm), (ii) falling BG trend at the end of the GST (lower BG at 180 min than at 120 min), (iii) hypoglycaemia and falling BG trend at the end of the GST, and (iv) at-risk patients (those with at least one of the three risks measures).

RESULTS

Twenty-seven of the 80 children had hypoglycaemia during the GST. Twenty-six children showed a falling BG trend at the end of the GST and were significantly younger than the other 54 children with a rising BG trend [5·1 (3·1-10·4) years vs 9·6 (5·4-11·8) years, P = 0·02]. Eight children had both a falling BG trend and hypoglycaemia at end of the test. Forty-four children were at-risk patients, and the odds ratio of being an at-risk patient in those <8 years old was 2·63 (95% CI 1·06-6·57, P = 0·04).

CONCLUSIONS

Hypoglycaemia is not uncommon during the low-dose GST. Young children, especially those <8 years old, are particularly at risk. BG monitoring should be considered essential from a safety perspective.

IGF-I and IGF Binding Protein-3 Generation Tests and Response to Growth Hormone in Children with Silver-Russell Syndrome

Objectives. To evaluate, in children with Silver-Russell Syndrome, the response to the IGF-I and IGFBP-3 generation test and compare results to the growth response after 6 months of rhGH. Methods. Eight children (6 males), with a mean age of 5.71 ± 2.48 years and height SDS of -3.88 ± 1.28 received rhGH for 6 months. IGF-I and IGFBP-3 were analyzed before and after 4 doses of rhGH. Results. The mean growth velocity (GV) before treatment was 5.28 ± 1.9 cm/year. GV increased after rhGH in five children to a mean GV of 10.3 ± 3.64 cm/year. Six children had normal basal IGF-I levels and two low levels. After 4 doses of rhGH, the IGF-I levels were normal in seven. There was no correlation between the growth response and the IGF-I generation test. Conclusions. Children with SRS have normal IGF-I generation test. There is no correlation between the generation test and the growth velocity after 6 months of rhGH.

Insulin-like growth factor-I in growth and metabolism

Deficiency of insulin-like growth factor-I (IGF-I) results in growth failure. A variety of molecular defects have been found to underlie severe primary IGF-I deficiency (IGFD), in which serum IGF-I concentrations are substantially decreased and fail to respond to GH therapy. Identification of more patients with primary or secondary IGFD is likely with investigative and diagnostic progress, particularly in the assessment of children with idiopathic short stature. Diagnosis of IGFD requires accurate and reliable IGF-I assays, adequate normative data for reference, and knowledge of IGF-I physiology for proper interpretation of data. Recombinant human IGF-I (rhIGF-I) treatment improves stature in patients with severe primary IGFD, and has also been shown to improve glycaemic control and insulin sensitivity in patients with severe insulin resistance. Ongoing studies of patients receiving rhIGF-I will allow further evaluation of the clinical utility of this treatment, with concurrent increase in our understanding of IGF-I and conditions of IGFD.

Profile of mecasermin for the long-term treatment of growth failure in children and adolescents with severe primary IGF-1 deficiency

Growth hormone insensitivity syndrome (GHI) or insulin-like growth factor-1 (IGF-1) deficiency (IGFD) is characterized by deficit of IGF-1 production due to alteration of response of growth hormone (GH) receptor to GH. This syndrome is due to mutation of GH receptor or IGF-1 gene and patients affected showed no response to GH therapy. The only treatment is recombinant IGF-1 (mecasermin), which has been available since 1986, but approved in the United States by the US Food and Drug Administration only in 2005 and in Europe by the European Medicines Agency in 2007. To date, few studies are available on long-term treatment with mecasermin in IGFD patients and some of them have a very small number of subjects. In this review we discuss briefly clinical features of severe primary IGFD, laboratory findings, and indications for treatment. Results of long-term therapy with rhIGF1 (mecasermin) in patients affected by severe primary IGFD and possible side effects are explained.

[Growth hormone and idiopathic short stature]

Idiopathic short stature is defined by height below 3rd percentile, in a child with normal birth height and weight, lack of dysmorphy, endocrine deficiency or systemic disease. Food and Drugs administration approved GH treatment in this indication in the United States, because it induces height gain, and sometimes may increase quality of life. There is no consensus in terms of duration, monitoring parameters, benefits and risks of long term GH treatment in these patients. Cost effectiveness of such a treatment is under debate, and ethical considerations also have to be taken into account. Recombinant IGF1 should not be proposed in this indication at the moment, due to the lack of sufficient data on potential GH insensitivity in a subgroup of these patients.

Idiopathic short stature: definition, epidemiology, and diagnostic evaluation

Idiopathic short stature is a condition in which the height of the individual is more than 2 SD below the corresponding mean height for a given age, sex and population, in whom no identifiable disorder is present. It can be subcategorized into familial and non-familial ISS, and according to pubertal delay. It should be differentiated from dysmorphic syndromes, skeletal dysplasias, short stature secondary to a small birth size (small for gestational age, SGA), and systemic and endocrine diseases. ISS is the diagnostic group that remains after excluding known conditions in short children.

Exon 3-deleted genotype of growth hormone receptor (GHRd3) positively influences IGF-1 increase at generation test in children with idiopathic short stature

CONTEXT

A GHR-exon 3 polymorphism has been reported to influence the growth response to hGH therapy in short stature children. None of these studies provided data on IGF-1 generation test.

OBJECTIVE

To evaluate the influence of the GHR-exon 3 polymorphism on the generation test in children with idiopathic short stature (ISS).

DESIGN AND PATIENTS

A total of 45 prepubertal ISS children were submitted to IGF-1 and IGFBP-3 generation test (4 days of hGH 33 microg/kg/day). Children were genotyped for GHR-exon 3: full-length (fl) and exon 3-deleted (d3) alleles.

MEASUREMENTS

IGF-1 and IGFBP-3 increment as absolute values and standard deviation scores (SDS).

RESULTS

Basal clinical and laboratory data were similar among patients with different genotypes (fl/fl vs. fl/d3 or d3/d3). All patients presented IGF-1 increase >or= 15 microg/l at generation test. Children with GHRd3 allele, as a group, presented a statistically significant higher IGF-1 SDS increase at generation test than children homozygous for GHRfl allele (1.0 ranging from 0.1 to 3.7 for fl/fl vs. 1.2 ranging from 0.3 to 4.4 for fl/d3 and d3/d3; P = 0.037). Multiple linear regression found a positive association between increase in IGF-1 SDS with chronological age (P = 0.007) and GHR genotype (P = 0.027), which together explain 24% of the variability of IGF-1 SDS increment at generation test. There was no difference in IGFBP-3 generation test between the two genotype groups.

CONCLUSION

This study demonstrates that ISS children carrying the GHRd3 allele, as a group, present a slightly higher GH sensitivity regarding short-term IGF-1 generation during hGH stimulus than children homozygous for GHRfl allele.

Short stature and decreased insulin-like growth factor I (IGF-I)/growth hormone (GH)-ratio in an adult GH-deficient patient pointing to additional partial GH insensitivity due to a R179C mutation of the growth hormone receptor

OBJECTIVE

Genetic factors play an expanding role in understanding growth hormone (GH) disorders, therefore the German KIMS Pharmacogenetics Study was initiated with the aim of genotyping various GH-/IGF-I-axis-related genes of GH-deficient adult patients to investigate genotype:phenotype relationships and response to GH therapy.

PATIENTS AND METHODS

129 consecutively enrolled GH-deficient adult patients were genotyped for variant 1 (V1) of the alternatively spliced noncoding exons in the 5'-untranslated region and for the nine coding exons of the GH receptor (GHR) gene, which obviously play a striking role in the function of the GH-IGF-I-axis. After detection of a heterozygous, non-synonymous mutation R179C in exon 6 in one single patient with acquired GH-deficiency (GHD) in late adulthood, analysis of her clinical data followed, leading to the diagnosis of mild short stature (-1.5SD). For further endocrine evaluation, five pituitary stimulation tests (arginine) of this patient were statistically compared to stimulation tests (arginine) of ten GH-deficient control patients, retrospectively.

RESULTS

The formerly in patients with Laron syndrome and idiopathic short stature reported mutation R179C leads to an amino acid change from an arginine residue (codon CGC) to a cysteine residue (codon TGC) in position 179 of the extracellular domain of the GHR. Statistical analysis revealed significant decreased IGF-I/GH(0) ratio (p=0.004) and IGF-I/GH(max) ratio (p=0.001) of the index patient compared to the control patients, implying growth hormone resistance of the index patient at the level of the GHR, according to the detected R179C mutation.

CONCLUSIONS

This study reports on the unusual case of a patient with mild short stature, who acquired GHD in late adulthood due to a non-secreting pituitary adenoma and get additionally diagnosed for pre-existing growth hormone insensitivity due to a formerly in two short statured patients described, single, heterozygous, non-synonymous mutation in the GHR. Our findings support the theory that heterozygous mutations in the GHR gene can have mild phenotypical consequences.

IGF-I, IGFBP-3 and ALS generation test in Turner syndrome

OBJECTIVES

The pathophysiology of the short stature in girls with Turner syndrome (TS) is not well understood. The "IGF-I generation test" is used to assess the sensitivity to growth hormone. We compared the biochemical response to four days of growth hormone of TS and controls.

STUDY DESIGN

Pre-pubertal TS were recruited to participate in the study. Their siblings served as controls. IGF-I, IGFBP-3 and ALS were measured before and 5 days after using hGH (0.05mg/kg/day). Student-t test was used to compare the differences in their responses.

RESULTS

Eleven TS (mean age of 8.5+/-2.4) and 11 siblings (6 females and 5 males) (mean age of 7.0+/-2.0) participated in the study. The basal serum levels of IGF-I, IGFBP-3 and ALS were normal and not different between groups (p=0.62 for IGF-I, p=0.91 for IGFBP-3 and p=0.51 for ALS). The IGF-I generation test was positive in all controls and in 10/11 TS. The IGFBP-3 generation test was positive in 6/11 controls and 4/11 TS. After hGH the mean IGFBP-3 was lower in TS than in controls (p=0.08). The ALS response to hGH was not uniform between groups.

CONCLUSIONS

The IGF-I and ALS generation test results were not different between controls and TS. The IGFBP-3 results were higher in the control group but more than 50% of tested children did not pass. The IGF-I/IGFBP-3 generation tests, as presently done, did not help in the understanding of the short stature in TS. The use of different GH dosages and number of doses need to be investigated.

Growth hormone treatment of non-growth hormone-deficient growth disorders

Although a large body of data on efficacy and safety of growth hormone (GH) treatment for various non-growth hormone-deficient (GHD) growth disorders has accumulated from a combination of clinical trial and postmarketing sources in the last 20 years or more, there remain limitations. Clinical trial data have the advantage of direct comparison of well-matched, randomized patient groups receiving treatment (or not) under comparable conditions and, as such, provide the highest quality evidence of efficacy. Clinical trials, however, are typically too small for any statistically valid assessment for safety, which is more comprehensively addressed using postmarketing data. Consequently, while the efficacy of GH treatment in children with non-GHD growth disorders has been solidly established and, based on the combination of the rigor of the clinical trial data and numerical power of the postmarketing data, no major concerns exist regarding safety, additional long-term data are required.

The insulin-like growth factor-I response to growth hormone is increased in prepubertal children with obesity and tall stature

CONTEXT

Children with obesity [body mass index (BMI) > +2 sd score (SDS)] and children with constitutional tall stature [CTS; height > +2 SDS)] have normal-high serum IGF-I levels, associated with a low and broad range of GH secretion, respectively. This suggests increased sensitivity to GH, whereas children with idiopathic short stature (ISS; height < -2 SDS) are believed to have decreased GH sensitivity. OBJECTIVE, DESIGN, AND MAIN OUTCOME MEASURE: To compare the responsiveness to GH in 62 prepubertal children (43 females, 19 males) with obesity, CTS, or ISS and 26 controls (15 females, 11 males; height and BMI -2 to +2 SDS), we used an IGF-I generation test and studied the IGF-I concentration 24 h after a single injection of GH (2 mg/m2).

PATIENTS

Twenty patients with obesity, 20 with CTS, 22 with ISS, and 26 controls were studied. The mean age was 8.3 +/- 2.9 yr, with no difference in age or gender between groups.

RESULTS

Compared with controls, the mean IGF-I increment was 80% higher in obese children and 36% higher in tall children (P < 0.05 obese or tall vs. control children; P = 0.05 obese vs. tall children). Conversely, the IGF-I increment was similar in short compared with control children, despite a mean baseline IGF-I 62% lower in short children (P < 0.05 vs. controls). In all groups, the IGF-I increment was correlated with the BMI SDS or the fat mass percentage (r = 0.51-0.58, P < 0.05).

CONCLUSION

Obese children tend to have greater GH responsiveness than tall children, and both have greater GH responsiveness than controls. GH responsiveness was similar in controls and short children, despite a lower baseline IGF-I in short children. Whether the differences in the IGF-I response to GH between these children reflect differences in the respective anabolic (growth promotion) and metabolic (i.e. insulin action modulation) roles of circulating IGF-I is unknown.

Controversy in clinical endocrinology: problems with reclassification of insulin-like growth factor I production and action disorders

CONTEXT

Recent developments in the IGF field have raised questions on whether this is the right time to redefine IGF deficiency.

OBJECTIVE

In this controversy, arguments are made against the need for redefining IGF deficiency at this moment, suggesting instead to wait for further clinical developments.

CASE

Although a number of rare case reports of IGF deficiency with precise molecular etiologies have been described, the vast majority of the cases remain clinically defined and without a genetic diagnosis.

INTERVENTIONS

Because IGF products are now available for clinical use in IGF-deficient patients, we are still using GH stimulation and static IGF levels as our only clinical diagnostic and classification tools. POSITIONS: We need to develop additional clinical tools, side by side with molecular tools, for the diagnosis and subclassification of IGF deficiency. Chief among these are the IGF-generation test for identification of GH-insensitive patients and genetic panels of polymorphic changes in relevant genes.

CONCLUSIONS

Until further progress is made in the clinical classification of IGF deficiency, we should not change the current classification, and, when we do, it should be the responsibility of the relevant societies in the field to conduct a consensus statement on the topic first.

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.

IGF-I and IGF Binding Protein-3 Levels during Initial GH Dosage Step-Up Are Indicators of GH Sensitivity in GH-Deficient Children and Short Children Born Small for Gestational Age

BACKGROUND

A stepwise increment of the GH dose is an approach aimed at avoiding adverse events. We investigated GH sensitivity by studying IGF-I and IGFBP-3 concentrations during the initial phase of GH treatment.

METHODS

Our investigation was part of the regular follow-up of prepubertal children with GH deficiency (GHD) (n = 31) and small for gestational age (SGA) (n = 23). Dosage was increased in three steps: one-third at the start, two-thirds after 14 days, and the full dose after 28 days (full dose: GHD = 28 microg/kg body weight (BW)/day; SGA = 60 microg/kg BW/day). Blood samples were taken on days 0, 14 and 28, as well as in conjunction with anthropometrical examinations after 3, 6 and 12 months. IGF-I and IGFBP-3 were measured by means of published in-house RIAs and age-related references were used to calculate standard deviation scores (SDS). Height velocity (cm/year) and Delta HT SDS were taken as growth response parameters.

RESULTS

Before GH treatment (GHD vs. SGA; median and p values): age (years) (6.6 vs. 6.0; n.s.), HT SDS (-2.6 vs. -3.2; p < 0.05); GH amount after stepping up (mug/kg BW/day) (28 vs. 60; p < 0.01); BW SDS (-0.5 vs. -2.9; p < 0.01); max. GH stimulated (microg/l) (5.6 vs. 10.8; p < 0.01); IGF-I SDS (-3.5 vs. -1.8; p < 0.01); IGFBP-3 SDS (-2.0 vs. 0.8; p < 0.01). After 1 year of GH therapy: HT velocity (cm/year) (9.8 vs. 9.6; n.s.), Delta HT SDS (0.9 vs. 0.9; n.s.); WT velocity (kg/year) (3.3 vs. 3.5; n.s.). Our results show that changes in growth similar to GHD could be induced in SGA by a dosage that was twice as high as the replacement dose given in GHD. GH dose and HT velocity did not correlate in both groups. IGF-I and IGFBP-3 increased as follows in GHD and SGA during stepping up of the dosage (ng/ml, GHD vs. SGA): at start, 54 vs. 89; at day 14, 78 vs. 132; at day 28, 90 vs. 167; at 3 months, 118 vs. 218. There was the same relationship between dose levels and absolute IGF-I concentrations in both groups. In terms of IGF-I SDS, the dose-response curve in SGA showed a shift to the right in comparison to GHD, thus indicating lower sensitivity to GH. The dynamics of IGF-I and IGFBP-3 differed, as IGFBP-3 peaked earlier (on day 28). In GHD, IGF-I SDS at 3 months was -0.7 vs. +0.9 in SGA. Near-identical levels were found for Delta IGF-I SDS and IGFBP-3 SDS above basal levels for each time-point investigated. First year HT velocity in GHD correlated negatively with basal IGF-I SDS (R(2) = 0.33; p <0.001) and basal IGFBP-3 (R(2) = 0.17; p <0.05) but did not correlate with the IGF-I increment during the 0- to 3-month period. Conversely, first year HT velocity correlated (+) in SGA with the IGF SDS increment during the 0- to 3-month period (R(2) = 0.26; p = <0.05). Height velocity in SGA, however, correlated neither with basal IGF-I and IGFBP-3 nor with the 0- to 3-month increments of IGFBP-3 SDS.

CONCLUSIONS

IGFs increase during initial GH therapy, thus raising questions about short-term IGF generation tests. (I) In terms of IGF generation, substantially lower sensitivity to GH was observable in SGA. (II) Higher GH sensitivity during first year catch-up growth is associated with GHD, but in SGA it is attributable to increases in IGF. A wider range of GH dosages needs to be explored in order to gain further insight into the relationship between GH dose, IGF levels, and growth. Monitoring IGFs is a practical means for exploring GH sensitivity during dosage stepping up.

Idiopathic short stature

The diagnostic term, idiopathic short stature, has emerged over the past 30 years and refers to children with short stature of unknown etiology. Controversy exists regarding the scope of the diagnosis and options for its treatment. This article reviews origins of the diagnosis idiopathic short stature and current diagnostic criteria, scientific advances in delineating etiologies of idiopathic short stature, management options, and implications of management decisions for child health.

Insulin-like growth factor I (IGF-I) measurements in growth hormone (GH) therapy of idiopathic short stature (ISS)

Growth hormone (GH) therapy has evolved rapidly over the past decade. Ongoing research has demonstrated a clear role for therapeutic GH in a wide spectrum of pediatric disorders involving both poor growth and abnormal body composition. Although guidelines for GH dosing are not fully established, a series of key studies has delineated the range of dosages that are useful in the treatment of children with growth disorders. The recent approval of idiopathic short stature (ISS) as an indication for GH therapy presents further challenges in optimizing the care of GH-treated patients. ISS is now recognized as a diverse collection of environmental and molecular abnormalities, some of which involve the GH-IGF axis. Emerging data indicate that serum IGF-I measurements are not only useful in the diagnosis of growth abnormalities but, in conjunction with auxological measurements, are also a powerful tool for assessing GH efficacy. While it is clear that many ISS patients respond to GH, some individuals will not show a satisfactory response. Monitoring IGF-I levels and change in height SDS during treatment can assist the physician in distinguishing those patients in whom GH successfully and safely induces statural growth from those with partial or complete GH insensitivity who might benefit from modified GH treatment protocols or alternate therapies. In addition, serum IGF-I measurements are increasingly used as part of a rational monitoring strategy to ensure safety of GH dosing in light of cumulative data associating high IGF-I levels with potential malignancy risk, and low IGF-I levels with cardiovascular disease risk.

Therapeutic applications of the insulin-like growth factors

The potential therapeutic applications of the insulin-like growth factors (IGFs) are broad. This review focuses on treatment of humans with recombinant human IGF-I (rhIGF-I), and with a rhIGF-I/IGF binding protein-3 (IGFBP-3) complex. Several groups of patients have been treated effectively, including individuals with growth hormone insensitivity syndrome (GHIS) secondary to GH receptor deficiency, to IGF-I gene deletion, or to defects in GH signal transduction pathways, patients with type 1 and type 2 diabetes mellitus, or individuals with severe insulin resistance syndromes. In each of these conditions rhIGF-I therapy has been demonstrated to be of clear clinical benefit. Other conditions, which may potential targets for therapy with rhIGF-I or rhIGF-I/IGFBP-3, include chronic inflammatory or nutritional disorders such as Crohn's disease, juvenile chronic arthritis, or cystic fibrosis. Therapy with IGFs has not been attempted in these disorders yet, in part because of lack of adequate supplies. Recently, the newly developed rhIGF-I/IGFBP-3 complex has been used in early clinical studies. Pharmacokinetic analyses in patients with diabetes mellitus and GHIS have suggested that a more physiological profile of serum IGF-I results. Improved glycaemic control has been reported in type 1 and type 2 diabetes in adults. A therapeutic trial in naïve children with GHIS is currently under way.