Heterozygous nonsense mutation in exon 3 of the growth hormone receptor (GHR) in severe GH insensitivity (Laron syndrome) and the issue of the origin and function of the GHRd3 isoform

Detecting novel Indel variants within the GHR gene and their associations with growth traits in Luxi Blackhead sheep

The growth hormone is important in the regulation of metabolism and energy homeostasis and acts through a growth hormone receptor (GHR). In this work, genetic variations within the ovine GHR gene were identified and tested for associations with body morphometric traits in Chinese Luxi Blackhead (LXBH) sheep. Novel deletion loci in the LXBH GHR gene included P2-del-23 bp and P8-del-23 bp indel variants. The polymorphic information content (PIC) was 0.329 in P2-del-23 bp and 0.257 in P8-del-23 bp. Moreover, both indel polymorphisms were not at Hardy-Weinberg equilibrium (p < 0.05) in the LXBH population. Statistical analyses revealed that the P2-del-23 bp and P8-del-23 bp indels were significantly associated (p < 0.05) with several growth traits in rams and ewes, including body weight, body height, chest depth, chest width, chest circumference, cannon circumference, paunch girth and hip width. Among the tested sheep, the body traits of those with genotype DD were superior to those with II and ID genotypes, suggesting that the 'D' allele was responsible for the positive effects on growth traits. Thus, these results indicate that the P2-del-23 bp and P8-del-23 bp indel sites and the DD genotype can be useful in marker-assisted selection in sheep.

Sequential measurements of IGF-I serum concentrations in adolescents with Laron syndrome treated with recombinant human IGF-I (rhIGF-I)

Background Recombinant human insulin-like growth factor 1 (rhIGF-I) has been approved as an orphan drug for the treatment of growth failure in children and adolescents with severe primary IGF-I deficiency (SPIGFD) with little pharmacokinetic data available. Therefore, sequential measurements of serum IGF-I, glucose, potassium, insulin and cortisol were performed in patients treated with rhIGF-I to evaluate their significance in safety and efficacy. Methods Repetitive blood samples were taken after meals before and 30, 60, 120, 180 and 360 min after rhIGF-I injections in two male patients with Laron syndrome at times of dose adjustments. Results Maximal IGF-I concentrations were observed 2 h after injections (495 ng/mL) and concentrations were still higher 6 h after injections than at baseline (303 ng/mL vs. 137 ng/mL). Thirteen percent of all and 33% of maximum IGF-I concentrations were greater than +2 standard deviation score (SDS) calculated for bone age (BA) (IGF-I SDS BA) rather than chronological age (CA) as BA was significantly delayed to CA by 3.2 years (p=0.0007). Height velocities correlated with individual maximum IGF-I SDS BA (ρ=0.735; p<0.0001). Serum insulin, cortisol and glucose did not correlate with IGF-I concentrations, but serum potassium showed a negative correlation (ρ=-0.364; p<0.0001) with IGF-I concentrations. Conclusions Sequential measurements of serum IGF-I, glucose and potassium in patients with Laron syndrome may aid in optimizing and individualizing rhIGF-I treatment. IGF-I concentrations should be referenced according to BA which better reflects the biological age. The inverse correlation of IGF-I and serum potassium concentrations after injections of rhIGF-I has not been reported before and warrants further consideration.

MECHANISMS IN ENDOCRINOLOGY: Clinical and pharmacogenetic aspects of the growth hormone receptor polymorphism

Pharmacogenetics aims to maximize the beneficial effects of a medical therapy by identifying genetic finger prints from responders and non-responders and, thereby improving safety and efficacy profile of the drug. Most subjects who are deficient in growth hormone (GHD) are candidates for recombinant human GH (rhGH) therapy. To date, it is well established that even after adjustments for several clinical variables, such as age, gender, body composition and the age at onset of the GHD, response to rhGH treatment is highly variable among individuals, part of which is believed to be due to genetic factors within the GH system. As the first genetic variant to potentially influence the individual response to rhGH therapy in children with growth disorders, polymorphism in the GH receptor (GHR) has attracted a great interest as a target for pharmacogenetics. Studies have been conducted to compare the functional and molecular effects of the full-length GHR (fl-GHR) isoform with the exon 3 deleted (d3-GHR) isoform in children and adults treated with rhGH therapy. Additionally, the impact of the GHR polymorphism has been investigated in relation to the clinical status and response to medical treatment in acromegaly, especially to the GHR antagonist drug pegvisomant. We have performed a narrative review of the studies performed to date on the association of GHR polymorphism with rhGH response in children and adults, and its potential influence in the medical management of acromegaly. In addition, data from studies on the general population and in other chronic diseases examining a role of this genetic variant in the regulation of growth and metabolism are summarized.

The GH receptor exon 3 deletion is a marker of male-specific exceptional longevity associated with increased GH sensitivity and taller stature

Although both growth hormone (GH) and insulin-like growth factor 1 (IGF-1) signaling were shown to regulate life span in lower organisms, the role of GH signaling in human longevity remains unclear. Because a GH receptor exon 3 deletion (d3-GHR) appears to modulate GH sensitivity in humans, we hypothesized that this polymorphism could play a role in human longevity. We report a linear increased prevalence of d3-GHR homozygosity with age in four independent cohorts of long-lived individuals: 841 participants [567 of the Longevity Genes Project (LGP) (8% increase; P = 0.01), 152 of the Old Order Amish (16% increase; P = 0.02), 61 of the Cardiovascular Health Study (14.2% increase; P = 0.14), and 61 of the French Long-Lived Study (23.5% increase; P = 0.02)]. In addition, mega analysis of males in all cohorts resulted in a significant positive trend with age (26% increase; P = 0.007), suggesting sexual dimorphism for GH action in longevity. Further, on average, LGP d3/d3 homozygotes were 1 inch taller than the wild-type (WT) allele carriers (P = 0.05) and also showed lower serum IGF-1 levels (P = 0.003). Multivariate regression analysis indicated that the presence of d3/d3 genotype adds approximately 10 years to life span. The LGP d3/d3-GHR transformed lymphocytes exhibited superior growth and extracellular signal-regulated kinase activation, to GH treatment relative to WT GHR lymphocytes (P < 0.01), indicating a GH dose response. The d3-GHR variant is a common genetic polymorphism that modulates GH responsiveness throughout the life span and positively affects male longevity.

siRNA-targeted inhibition of growth hormone receptor in human colon cancer SW480 cells

AIM: To determine the effects of RNAi-mediated inhibition of the growth hormone receptor (GHR) gene on tumors and colon cancer cells in vivo.

METHODS: Construction of a eukaryotic vector for human GHR expression, the pcDNA™6.2-GW/EmGFP-small interfering RNAs (siRNAs)-GHR plasmid, was used to inhibit GHR expression. Thirty-six BALB/c nude mice were randomly divided into groups and treated with normal saline (NS), recombinant plasmid (G₂), growth hormone (GH), 5-fluorouracil (FU), G₂+FU or G₂+FU+GH. Each nude mouse was subcutaneously inoculated with 1×10⁷ human colon cancer SW480 cells; the nude mice were weighed before inoculation and on the 2^nd, 5^th, 8^th, 11^th, 14^th and 17^th day after inoculation. All nude mice were sacrificed after 17 d. Each subcutaneous tumor was removed and studied. Tumor volume was measured on the 5^th, 8^th, 11^th, 14^th and 17^th day after inoculation. The expression of GHR protein in the tumor tissue was detected by Western blotting analysis, and the differences in GHR mRNA expression in the tumor tissue were detected by real-time quantitative reverse transcription-polymerase chain reaction.

RESULTS: Compared to the control group, the weights of the inoculated nude mice on the 17^th day after inoculation were: G₂: 21.60 ± 0.71 g, GH: 21.64 ± 0.45 g, FU: 18.94 ± 0.47 g, FU+G₂: 19.40 ± 0.60 g, G₂+FU+GH: 21.04 ± 0.78 g vs NS: 20.68 ± 0.66 g, P < 0.05; the tumor volumes after the subcutaneous inoculation were: G₂: 9.71 ± 3.82 mm³, FU: 11.54 ± 2.42 mm³, FU+G₂: 11.42 ± 1.11 mm³, G₂+FU+GH: 10.47 ± 1.02 mm³vs NS: 116.81 ± 10.61 mm³, P < 0.05. Compared to the GH group, the tumor volumes were significantly decreased in the experimental groups. The GHR protein expression (G₂: 0.39 ± 0.02, FU: 0.40 ± 0.02, FU+G₂: 0.38 ± 0.01, G₂+FU+GH: 0.39 ± 0.01 vs NS: 0.94 ± 0.02, P < 0.05) and the GHR mRNA expression (G₂: 14.12 ± 0.10, FU: 15.15 ± 0.44, FU+G₂: 16.46 ± 0.27, G₂+FU+GH: 15.37 ± 0.57 vs NS: 12.63 ± 0.14, P < 0.05) were significantly decreased and increased, respectively, in the experimental groups.

CONCLUSION: Inhibition of GHR in human colon cancer SW480 cells resulted in anti-tumor effects in nude mice.

Growth hormone insensitivity syndrome caused by a heterozygous GHR mutation: phenotypic variability owing to moderation by nonsense-mediated decay

OBJECTIVES

Growth hormone insensitivity syndrome (GHIS) is characterized by extreme short stature and resistance to the actions of growth hormone (GH). The heterogeneity ranges from the most severe form, known as Laron syndrome, to less severe phenotypes like idiopathic short stature and partial GH insensitivity. Here, we aimed to identify and characterize the molecular cause of severe short stature in a patient with resistance to GH treatment.

PATIENT

We describe a male patient born small for gestational age [38 weeks gestation, length 38·5 cm; -7·8 standard deviation score (SDS), weight 1350 g; -4·84 SDS]. At the age of 7 years (109·7 cm; -2·89 SD), he received GH treatment (1 mg/m(2)/day) for 1 year without any increase in height SDS, IGF-I or IGFBP-3 levels. Double-GH-dose treatment for another year did not result in any improvement in growth factor level either. The patient does not have the typical Laron craniofacial and somatic features.

RESULTS

Analysis of GHR showed a heterozygous nonsense mutation (c.703C>T; p.Arg217X). Extensive mutation screening as well as copy number variation analysis of other candidate genes in the GH-IGF-I axis excluded any additional genetic defects. Analysis of the patient's fibroblasts showed that growth hormone receptor (GHR) messenger ribonucleic acid (mRNA) expressed from the mutant allele was degraded by a mechanism called nonsense-mediated mRNA decay (NMD).

CONCLUSIONS

GHIS in this patient is because of a heterozygous nonsense mutation in GHR. Our study is the first to demonstrate that NMD is involved in the phenotypic variability of GHIS caused by GHR mutations.

Maturation of the growth axis in marsupials occurs gradually during post-natal life and over an equivalent developmental stage relative to eutherian species

The separation of a nutrition-responsive insulin-like growth factor (IGF) system and a growth hormone (GH) responsive IGF system to control pre- and post-natal growth of developing mammals may originate from the constraints imposed by intra-uterine development. In eutherian species that deliver relatively precocial young, maturation of the GH regulatory system is coincident with the time of birth. We measured the hepatic expression of the four key growth axis genes GH-receptor, IGF-1 and -2, and IGFBBP-3, and plasma protein concentrations of IGF-1 from late fetal life through to adult stages of a marsupial, the tammar wallaby. The data clearly show that maturation of GH-regulated growth in marsupials occurs gradually over the course of post-natal life at an equivalent developmental stage to that of precocial eutherian mammals. This suggests that the timing of GH-regulated growth in marsupials is not related to parturition but instead to the relative developmental stage.

The exon 3-deleted growth hormone receptor: molecular and functional characterization and impact on GH/IGF-I axis in physiological and pathological conditions

The GH receptor (GHR) plays a key role in the the function of the GH/IGF-I axis and is the major effector of human growth. A common polymorphic variant consisting of genomic exon 3 deletion or retention (d3-GHR and full-length GHR, respectively), described in 2000, has been linked with increased receptor activity due to enhanced signal transduction. Subsequent pharmacogenetic studies have addressed a possible role of GHR polymorphism on the response to recombinant human GH treatment first in short children and then in adults, many of them suggesting that growth response to GH may be influenced, at least in some aspects, by this polymorphism. Similar studies, performed in patients with acromegaly, assumed an influence of the d3- GHR variant in the relationship between GH and IGF-I levels. More recently, some studies have investigated the relation between GHR genotype and treatment with the GHR antagonist pegvisomant, suggesting a better clinical response to therapy related to d3-GHR genotype. This review provides a summary of the main pharmacogenetic studies performed on this current and still open topic.

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.

Genetics of GHRH, GHRH-receptor, GH and GH-receptor: its impact on pharmacogenetics

When a child is not following the normal, predicted growth curve, an evaluation for underlying illnesses and central nervous system abnormalities is required and, appropriate consideration should be given to genetic defects causing GH deficiency (GHD). Because Insulin-like-Growth Factor-I (IGF-I) plays a pivotal role, GHD could also be considered as a form of IGF-I deficiency (IGFD). Although IGFD can develop at any level of the GHRH-GH-IGF axis, a differentiation should be made between GHD (absent to low GH in circulation) and IGFD (normal to high GH in circulation). The main focus of this review is on the GH-gene, the various gene alterations and their possible impact on the pituitary gland. However, although transcription factors regulating the pituitary gland development may cause multiple pituitary hormone deficiency they may present initially as GHD. These defects are discussed in various different chapters within this book, whereas, the impact of alterations of the GHRH-, GHRH-receptor- --as well as the GH-receptor (GHR) gene--will be discussed here.

Genetic defects causing functional and structural isolated growth hormone deficiency

Normal somatic growth requires the integrated function of many of the hormonal, metabolic, and other growth factors involved in the hypothalamo-pituitary-somatotrope axis. Human growth hormone (hGH) causes a variety of physiological and metabolic effects in humans and its pivotal role in postnatal growth is undisputed. Disturbances that occur during this process often cause subnormal GH secretion and/or subnormal GH sensitivity/responsiveness resulting in short stature. Despite the complexity of this linear growth process, the growth pattern of children, if evaluated in the context of normal standards, is rather predictable. Children presenting with short stature (i.e out of normal standards) are treated with daily injections of recombinant human GH (rhGH), which leads in almost all cases to an increase of height velocity. Although it is becoming more and more evident that many genes are involved in controlling the regulation of growth, the main aim of this review is to focus on the GH-1 gene, the various gene alterations and their important physiological and pathophysiological role in growth.

The common exon 3 polymorphism of the growth hormone receptor gene and the effect of growth hormone therapy on growth in Korean patients with Turner syndrome

OBJECTIVE

Recombinant human growth hormone (GH) can achieve final adult height gain in girls with Turner syndrome (TS), but its efficacy varies widely across individuals. The exon 3-deleted polymorphism of growth hormone receptor (d3-GHR) has been reported to be associated with responsiveness to GH therapy. The short-term growth response of Turner patients to GH therapy was analysed according to their GHR-exon 3 polymorphism genotype.

DESIGN AND PATIENTS

This was a retrospective study of 175 TS patients. Auxological and endocrine parameters were measured, and the GHR-exon 3 genotype was analysed. Allelic frequencies of GHR-exon 3 genotype were compared between patients with TS and control individuals. GH had been administered to 147 patients, 115 of which remained pre-pubertal after the first follow-up year. Changes in height standard deviation score (SDS), height velocity (HV), body mass index (BMI), IGF-1 and IGF binding protein-3 (IGFBP-3) concentrations were compared between these patients, grouped according to genotype, after the first follow-up year.

RESULTS

There was no difference in GHR-exon 3 genotype frequency between the TS and control groups of Koreans. According to the GHR-exon 3 genotype (fl/fl group vs. d3/fl and d3/d3 group), HV gain and height SDS gain did not differ significantly at the first year of GH therapy. Moreover, changes in IGF-1, IGFBP-3 concentration and BMI showed no significant difference between the groups with and without d3-GHR after 1 year of GH therapy.

CONCLUSION

The distribution of the GHR-exon 3 genotype was similar in the TS and control groups in a Korean population. The growth promotion efficacy of GH therapy did not differ significantly between TS patients with and without the d3-GHR allele. These findings indicate that the GHR-exon 3 genotype may not be a major factor to affect the GH response in Korean Turner patients.

Impact of the exon 3-deleted growth hormone (GH) receptor polymorphism on baseline height and the growth response to recombinant human GH therapy in GH-deficient (GHD) and non-GHD children with short stature: a systematic review and meta-analysis

CONTEXT

The exon-3 deleted GH receptor (GHR(d3)) polymorphism is associated with an increased growth response to recombinant human GH (rhGH) therapy in some, but not all, studies in GH-deficient (GHD) and non-GHD children with short stature.

OBJECTIVE

The aim of the study was to assess the effects of GHR(d3) on baseline height and the first year's growth response to rhGH treatment in prepubertal GHD and non-GHD children with short stature.

DESIGN

We conducted a systematic review and meta-analysis.

METHODS

Fifteen studies reporting the effect of GHR(d3) on growth parameters were included. Principal outcomes were baseline height sd score (SDS) and the weighted average of change in growth velocity (Delta cm/yr) and height gain (Delta height SDS) after 1 yr of rhGH.

RESULTS

In GHD, not in non-GHD, baseline height SDS was 0.159 sd higher [95% confidence interval (CI), 0.020, 0.298] in GHR(d3) compared with GHR(wt-wt). In GHR(d3), rhGH therapy resulted in a higher increase in growth velocity (0.521 cm/yr; 95% CI, 0.196, 1.015) and height gain (0.075 sd; 95% CI, 0.007, 0.143) compared with GHR(wt-wt). Meta-regression demonstrated a larger difference between GHR(d3) and GHR(wt-wt) in studies using lower rhGH doses and carried out at a higher age, independently of the cause of short stature.

CONCLUSIONS

This meta-analysis in prepubertal children with short stature indicates that GHR(d3) is associated with increased baseline height in GHD, but not in non-GHD. Furthermore, GHR(d3) stimulates growth velocity by an additional effect of approximately 0.5 cm during the first year of rhGH treatment, and this effect is more pronounced at lower doses of rhGH and higher age.

Common exon 3 polymorphism of the GH receptor (GHR) gene and effect of GH therapy on growth in Korean children with idiopathic short stature (ISS)

OBJECTIVE

A human GH receptor (GHR) gene exon 3 polymorphism (d3-GHR) has been reported to be associated with responsiveness to GH therapy. We assessed the frequencies of this polymorphism in Korean control and idiopathic short stature (ISS) populations, and analysed short-term growth response to GH therapy according to GHR-exon 3 genotypes in Korean children with ISS.

DESIGN AND PATIENTS

This was a retrospective study in 158 ISS children. Auxological and endocrine parameters were measured, and the GHR-exon 3 genotype was analysed. Allelic frequencies of GHR-exon 3 genotype were compared between the ISS group and a control group. GH had been administered for 62 patients, 52 of whom remained prepubertal after the first follow-up year. Changes in height velocity (HV) and IGF-1 and IGFBP-3 concentrations following GH therapy were compared in patients with these genotypes.

RESULTS

There was no difference in GHR-exon 3 genotype frequency between ISS and control groups of Koreans. However, the fl/fl genotype was more frequent in Koreans than in Caucasians. ISS children with d3-GHR showed a significantly higher increment in HV (P = 0.002) and a marginally significant increment in IGF-1 concentration (P = 0.064) at the first year of GH therapy.

CONCLUSION

fl-GHR was more frequently detected in a Korean population than in Caucasians. The growth promotion efficacy of GH therapy differed significantly between ISS patients with and without the d3-GHR allele. These findings indicate that the GHR-exon 3 polymorphism can affect the growth promoting efficacy of short-term GH therapy in Korean children with ISS.

Exon 3 of the growth hormone receptor (GH-R) is specific to eutherian mammals

Growth hormone receptor (GH-R) plays a critical role in the control of growth and metabolism in all vertebrates. GH-R consists of 9 coding exons (2-10) in all eutherian mammals, while the chicken only has 8 coding exons, and does not have an orthologous region to exon 3 in eutherians. To further understand the evolutionary origins of exon 3 of the GH-R in eutherians we cloned the full-length GH-R sequence in a marsupial, the tammar wallaby to determine whether exon 3 was present or absent in marsupial liver cDNA. There was no evidence for the presence of an exon 3 containing mRNA in sequence of tammar pouch young and adult livers. We next examined the genomes of the platypus (a monotreme mammal) and the grey short-tailed opossum (another marsupial). Like the tammar, the GH-R gene of neither species contained an exon 3. GH receptor can obviously function in the absence of this exon, raising speculation about the function of this domain, if any, in eutherians. A comparison of exon 3 protein sequences within 16 species of eutherian mammals showed that there was approximately 75% homology in the domain but only 3 of the 21 amino acids were identical (Leu12, Gln13 and Pro17). Interestingly, we detected greater evolutionary divergence in exon 3 sequences from species that have variants of GH or prolactin (PRL) in their placentas. These data show that exon 3 was inserted into the GH-R after the divergence of the marsupial and eutherian lineages at least 130 million years ago.

Influence of growth hormone (GH) receptor deletion of exon 3 and full-length isoforms on GH response and final height in patients with severe GH deficiency

CONTEXT

A polymorphism of the GH receptor (GHR) gene resulting in genomic deletion of exon 3 (GHR-d3) has been associated with responsiveness to GH therapy. However, the data reported so far do vary according to the underlying condition, replacement dose, and duration of the treatment. OBJECTIVE, DESIGN: The aim of this study was to analyze the impact of the GHR genotypes in terms of the initial height velocity (HV) resulting from treatment and the impact upon adult height in patients suffering from severe isolated GH deficiency. CONTROLS, PATIENTS, SETTING: A total of 181 subjects (peak stimulated GH<or=2 ng/ml) were studied. In addition, GHR genotype frequency was compared with a healthy adult control group.

INTERVENTIONS

Based on the various GHR genotypes, HV, effect of recombinant human GH dose used, and final height were analyzed. MAIN OUTCOME MEASURES, RESULTS: In the 181 subjects after the first two yr on recombinant human GH treatment, HV sd score (SDS) as well as height gain were significantly greater in subjects with the GHR-d3/d3 genotype when compared with the subjects presenting with the GHR-full-length/full-length genotype (P<0.05). A GHR-d3 allele dose-dependent effect was found for both HV SDS (r=0.72) and height gain (r=0.77). However, there was no significant difference in final adult height and height SDS according to the exon-3 genotypes.

CONCLUSIONS

Our results indicate that in patients with severe isolated GH deficiency, although the GHR genotype might play a role in GH responsiveness, at least at the beginning of treatment, there is no effect on final height.

GHR exon 3 polymorphism: association with type 2 diabetes mellitus and metabolic disorder

Growth hormone (GH) signaling via the growth hormone receptor (GHR) forms a major part of the GH-IGF-I axis, which is crucial for controlling metabolism and anabolism. Two common variants of the GHR differ by the presence (full length or GHR(fl)) or absence of exon 3 (exon 3 deleted or GHR(d3)), the function of which is unknown. However, differential response to GH treatment has been observed with carriers of the GHR(d3) variant conferring a greater growth rate. This study investigates these GHR variants in subjects with normal glucose tolerance (NGT) and impaired glucose tolerance (IGT), including Type 2 diabetes mellitus (T2DM). DNA was extracted from blood samples from subjects with NGT (n=158), IGT (n=116) and T2DM (n=194). The T2DM subjects in set 1 (n= 39) were newly diagnosed, whilst those in set 2 (n=155) had a mean duration of 7 years. Set 1 also included NGT and IGT subjects. Genotyping by standard PCR and gel electrophoresis were carried out. A significant difference was observed between T2DM and NGT (p<0.0001) with a significantly lower frequency of GHR(d3) in T2DM (3.6% compared to 17% in NGT). Both sets of T2DM subjects with at least one GHR(d3) allele had significantly higher BMI. In the larger subset of T2DM, GHR(d3) was associated with higher CRP levels as well as age adjusted IGF-I, with a trend of higher C-peptide secretion and impaired lipid levels, indicating a phenotype with metabolic disorder when compared to the GHR(fl/fl) T2DM subjects. In conclusion, homozygosity for the GHR(d3) allele appears to be preventive of T2DM. However, when other factors cause overt T2DM, the GHR(d3) allele confers a phenotype indicative of metabolic disorder. This study supports the hypothesis that the two GHR alleles by their inclusion or exclusion of exon 3 are functionally different.

Common genetic variation in eight genes of the GH/IGF1 axis does not contribute to adult height variation

Stature (adult height) is one of the most heritable human traits, yet few genes, if any, have been convincingly associated with adult height variation in the general population. Here, we selected 150 tag SNPs from eight candidate genes in the growth hormone (GH)/insulin-like growth factor-1 (IGF1) axis (GHR, GHRH, GHRHR, IGF1, IGFALS, IGFBP3, JAK2, STAT5B), and genotyped them in approximately 2,200 individuals ascertained for short or tall stature. Nominally significant tag SNPs were then tested in three additional replication cohorts, including a family-based panel to rule out spurious associations owing to population stratification. Across the four height cohorts (N = 6,075 individuals), we did not observe any consistent associations between stature and common variants (> or =5% minor allele frequency) in these eight genes, including a common deletion of the growth hormone receptor gene exon 3. Tests of epistatic interactions between these genes did not yield any results beyond those expected by chance. Although we have not tested all genes in the GH/IGF1 axis, our results indicate that common variation in these GH/IGF1 axis genes is not a major determinant of stature, and suggest that if common variation contributes to adult height variation in the general population, the variants are in other, possibly unanticipated genes.

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.

Relationship between Nocturnal Growth Hormone Concentrations, Serum IGF-I/IGFBP-3 Levels, Insulin Sensitivity and GH Receptor Allelic Variant in Small for Gestational Age Children

Growth hormone may help to increase final height in patients with short stature, but its efficacy is variable. It has been recently reported that the isoform of the GH receptor (GHR) that lacks exon 3 (d3-GHR) is associated with a greater growth response to GH therapy. We hypothesized that nocturnal growth hormone concentrations, basal IGF-I and IGFBP-3 levels, and insulin sensitivity might show variations among individuals depending on their GHR allelic variant. To test this hypothesis, we studied 38 prepubertal LBW children with nocturnal GH concentrations, IGF-I and IGFBP-3 levels and insulin sensitivity during OGTT and Insulin test. The GHR allelic variant was analyzed through multiplex PCR analysis in DNA from peripheral leukocytes. Characteristics of the overnight GH secretion [(mean GH: 6.8 +/- 0.6 vs. 6.2 +/- 0.5 ng/ml), (AUC: 3,227 +/- 280 vs. 2,908 +/- 212 ng/ml.min), (peak number: 4.4 +/- 0.3 vs. 4.4 +/- 0.2), (amplitude: 12 +/- 1.1 vs. 10.8 +/- 1.1 ng/ml)] did not differ between groups (f1/f1 vs. f1/d3 plus d3/d3). In addition, we did not observe any significant differences in serum IGF-I SDS (-0.49 +/- 0.26 vs. -0.40 +/- 0.35) or IGFBP-3 SDS (-1.21 +/- 0.24 vs. -0.89 +/- 0.21) nor in insulin sensitivity (WIBSI: 12 +/- 1.2 vs. 10.8 +/- 1.1) in LBW children with full length GHR compared to children carrying at least one GHRd3 allele. The distribution of the f1/f1 allelic variant and fi/d3 or d3/d3 was similar in the LBW children with or without catch-up growth. These results suggest that the GHR allelic variant does not play a significant role in the regulation of GH-IGF-I/BP3 axis or in insulin sensitivity in prepubertal LBW children.

The growth hormone receptor in growth

The growth hormone receptor (GHR) is a major effector of Human growth. Functional variants of the GHR include very rare loss-of-function mutations (pathology) and very common polymorphisms (physiology). Recent experimental data have clarified the mechanisms through which mutations of the GHR or Stat5 lead to growth hormone insensitivity and major monogenic growth defects. Recent pharmacogenetic studies support that the response to growth-promoting administration of growth hormone is influenced by exon 3 polymorphism of the GHR.

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.

Growth Hormone Receptor Sequence Changes Do Not Play a Role in Determining Height in Children with Idiopathic Short Stature

BACKGROUND/AIMS

In children with short stature, in whom growth hormone deficiency has been excluded, the presence of a normal or elevated growth hormone concentration concomitant with low insulin-like growth factor I suggests growth hormone insensitivity (GHI). Previous reports suggest that heterozygous mutations in the growth hormone receptor gene (GHR) may account for about 5% of children with idiopathic short stature (ISS). In the present study we have attempted to determine whether mutations in the GHR explain the short stature and growth retardation in a cohort of children with ISS and characteristics suggesting GHI.

METHODS

For the present study 33 children with clinical and biochemical characteristics of GHI were selected from a cohort of 150 children of short stature. Molecular analysis of the GHR was performed using a single-strand conformation polymorphism technique and sequencing. Ten different sequence changes in 19 (58%) out of 33 children were identified, 9 of them novel and 1 that had been described previously.

RESULTS

Two changes were found in exons 2 and 6. The known polymorphism of exon 6 (G168) was significantly more common in the control subjects than in our study group (63.5 vs. 30%; p < 0.0001). In the intronic sequences 8 previously undescribed DNA changes were found. The screening of the affected children's family members revealed that both normal and short stature members carried the same variants. The study group did not significantly differ from the controls in retention (GHRfl) or exclusion (GHRd3) of exon 3.

CONCLUSION

Our study suggests that sequence changes of the GHR are common in children with ISS. The presence of these sequence changes in the control subjects as well as in normal stature family members indicates that these changes represent a simple polymorphism of the GHR. Such DNA changes are more prevalent than previously recognized, and they do not seem to play a contributory role in the etiology of short stature.

Physiology and pathophysiology of growth hormone-binding protein: methodological and clinical aspects

Circulating GH is partly bound to a high-affinity binding protein (GHBP), which in humans is derived from cleavage of the extracellular domain of the GH receptor. The precise biological function GHBP is unknown, although a regulation of GH bioactivity appears plausible. GHBP levels are determined by GH secretory status, body composition, age, and sex hormones, but the cause-effect relationships remain unclarified. In addition to the possible in vivo significance of GHBP, the interaction between GH and GHBP has methodological implications for both GH and GHBP assays. The present review concentrates on methodological aspects of GHBP measurements, GHBP levels in certain clinical conditions with a special emphasis on disturbances in the GH-IGF axis, and discusses the possible relationship between plasma GHBP and GH receptor status in peripheral tissues.

A common polymorphism of the growth hormone receptor is associated with increased responsiveness to growth hormone

Growth hormone is used to increase height in short children who are not deficient in growth hormone, but its efficacy varies largely across individuals. The genetic factors responsible for this variation are entirely unknown. In two cohorts of short children treated with growth hormone, we found that an isoform of the growth hormone receptor gene that lacks exon 3 (d3-GHR) was associated with 1.7 to 2 times more growth acceleration induced by growth hormone than the full-length isoform (P < 0.0001). In transfection experiments, the transduction of growth hormone signaling through d3-GHR homo- or heterodimers was approximately 30% higher than through full-length GHR homodimers (P < 0.0001). One-half of Europeans are hetero- or homozygous with respect to the allele encoding the d3-GHR isoform, which is dominant over the full-length isoform. These observations suggest that the polymorphism in exon 3 of GHR is important in growth hormone pharmacogenetics.