Growth hormone insensitivity

Challenges in the Management of Short Stature

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

[Physiology of the GH-IGF axis]

Growth, the main characteristic of childhood and adolescence, has a similar pattern in the majority of the individuals. Genetic background and GH-IGF axis are the factors that directly influence this process. Pituitary GH acts on growth mainly through the regulation of IGF system. The IGFs (IGF-1 and IGF-2) are growth factors produced in the majority of the organs and body tissues. They have autocrine, paracrine and endocrine actions on metabolism and cell proliferation, growth and differentiation. The IGFs bind with high specificity and affinity to a family of 6 binding proteins, called IGFBPs (1 to 6) that modulate their bioactivity. Most of the known IGF actions are mediated via IGF type 1 receptor (IGF1R). In this article we are going to review the composition and regulation of the GH-IGF axis and the role of each component in the regulation of the growth process.

A novel growth hormone receptor gene deletion mutation in a patient with primary growth hormone insensitivity syndrome (Laron syndrome)

OBJECTIVE

Growth hormone (GH) insensitivity syndrome (Laron syndrome) is known to be caused by genetic disorders of the GH-IGF-1 axis. Although many mutations in the GH receptor have been identified, there have been only a few reports of deletions of the GH receptor gene.

DESIGN

A Japanese adult female patient with Laron syndrome was subjected to chromosome analysis with basic G-banding and also with a high accuracy technique. Each exon of the GH receptor gene was amplified by means of PCR. Since this patient was diagnosed with osteoporosis, the effects of alendronate on bone mineral density (BMD) were also examined.

RESULTS

The chromosome analysis with the high accuracy technique demonstrated a large deletion of the short arm in one allele of chromosome 5 from p11 to p13.1 [46, XX, del (5) (p11-p13.1)]. PCR amplification of exons of the GH receptor gene showed that only exons 2 and 3 were amplified. Low-dose IGF-1 administration (30microg/kg body weight) failed to increase her BMD, whereas alendronate administration resulted in an increase associated with a decrease in urinary deoxypyridinoline (DPD) and serum osteocalcin concentrations.

CONCLUSIONS

The GH receptor gene of the patient was shown to lack exons 4-10. To the best of our knowledge, this is the third case report of Laron syndrome with large GH receptor deletion. Alendronate was effective for the enhancement of BMD.

Abnormalities of the axial and proximal appendicular skeleton in adults with Laron syndrome (growth hormone insensitivity)

OBJECTIVE

To investigate abnormalities in the skeleton (with the exclusion of the skull, cervical spine, hands and feet) in patients with Laron syndrome, who have an inborn growth hormone resistance and congenital insulin-like growth factor-1 (IGF-1) deficiency.

DESIGN AND PATIENTS

The study group was composed of 15 untreated patients with Laron syndrome (seven male and eight female) aged 21-68 years. Plain films of the axial and appendicular skeleton were evaluated retrospectively for abnormalities in structure and shape. The cortical width of the long bones was evaluated qualitatively and quantitatively (in the upper humerus and mid-femur), and the cortical index was calculated and compared with published references. Measurements were taken of the mid-anteroposterior and cranio-caudal diameters of the vertebral body and spinous process at L3, the interpedicular distance at L1 and L5, and the sacral slope. Thoracic and lumbar osteophytes were graded on a 5-point scale. Values were compared with a control group of 20 healthy persons matched for age.

RESULTS

The skeleton appeared small in all patients. No signs of osteopenia were visible. The cortex of the long bones appeared thick in the upper limbs in 11 patients and in the lower limbs in four. Compared with the reference values, the cortical width was thicker than average in the humerus and thinner in the femur. The vertebral diameters at L3 and the interpedicular distances at L1 and L5 were significantly smaller in the patients than in the control subjects (P<0.001); however, at L5 the canal was wider, relative to the vertebral body. The study group had a higher rate of anterior osteophytes in the lumbar spine than the controls had, and their osteophytes were also significantly larger. In the six patients for whom radiographs of the upper extremity in its entirety were available on one film, the ulna appeared to be rotated. In one 22-year-old man, multiple epiphyses were still open.

CONCLUSION

Congenital IGF-1 deficiency leads to skeletal abnormalities characterized by small bones, narrow spinal canal, and delayed bone age. The limitation in elbow distensibility common to patients with Laron syndrome may be related to a marked retroversion of the humeral head.

Interaction of GH polymorphism with body weight and endocrine functions in Japanese black calves

We assessed the interaction of GH gene polymorphisms (AA, AB and BB genotypes) with body weight and measures of endocrine function in Japanese black calves at 10 months of age. The average body weight for the BB genotype (281+/-5 kg) was significantly lower (P=0.0017, ANOVA) than those for the AA (324+/-9 kg) and AB (317+/-7 kg) genotypes. Plasma concentrations of insulin and IGF-I were greater for the AA genotype than for the AB genotype, and AB and BB genotypes, respectively. There were significant differences in the triglyceride and cholesterol concentrations among the GH genotypes. The area under the basal GH concentration was significantly greater (P=0.0314) for the AA genotype than for the two other genotypes. The incremental area over the basal GH concentrations in response to intravenous GHRH injection (0.4 microg/kg BW) was significantly smaller (P=0.0005) for the BB genotype than for the two other genotypes. In addition, linear regression analysis between GH incremental area induced by GHRH and body weight demonstrated that there was a positive linear correlation (r=0.6496, P<0.002) for incremental areas less than 600 ng min/ml, but a negative correlation (r=0.6473, P<0.05) for incremental areas over 600 ng min/ml. These findings indicate that the GH genotypes of the animals could be associated with difference in the GH response in Japanese black cattle at 10 months of age. We also observed a relationship between genotype and animal performances, but other studies on more animals in different conditions must be realized to make a definite conclusion.

Long-term treatment with recombinant insulin-like growth factor (IGF)-I in children with severe IGF-I deficiency due to growth hormone insensitivity

CONTEXT

Children with severe IGF-I deficiency due to congenital or acquired defects in GH action have short stature that cannot be remedied by GH treatment.

OBJECTIVES

The objective of the study was to examine the long-term efficacy and safety of recombinant human IGF-I (rhIGF-I) therapy for short children with severe IGF-I deficiency.

DESIGN

Seventy-six children with IGF-I deficiency due to GH insensitivity were treated with rhIGF-I for up to 12 yr under a predominantly open-label design.

SETTING

The study was conducted at general clinical research centers and with collaborating endocrinologists.

SUBJECTS

Entry criteria included: age older than 2 yr, sd scores for height and circulating IGF-I concentration less than -2 for age and sex, and evidence of resistance to GH.

INTERVENTION

rhIGF-I was administered sc in doses between 60 and 120 microg/kg twice daily.

MAIN OUTCOME MEASURES

Height velocity, skeletal maturation, and adverse events were measured.

RESULTS

Height velocity increased from 2.8 cm/yr on average at baseline to 8.0 cm/yr during the first year of treatment (P < 0.0001) and was dependent on the dose administered. Height velocities were lower during subsequent years but remained above baseline for up to 8 yr. The most common adverse event was hypoglycemia, which was observed both before and during therapy. It was reported by 49% of treated subjects. The next most common adverse events were injection site lipohypertrophy (32%) and tonsillar/adenoidal hypertrophy (22%).

CONCLUSIONS

Treatment with rhIGF-I stimulates linear growth in children with severe IGF-I deficiency due to GH insensitivity. Adverse events are common but are rarely of sufficient severity to interrupt or modify treatment.

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.

Aberrant Folding of a Mutant Stat5b Causes Growth Hormone Insensitivity and Proteasomal Dysfunction

A predicted alanine to proline substitution in Stat5b that results in profound short stature, growth hormone insensitivity, and immunodeficiency represents the first natural mutation of this transcription factor in a human. To understand the mechanisms responsible for these pathophysiological abnormalities, we have studied the biochemical and biophysical properties of the mutant Stat5b molecule. In a cellular reconstitution model growth hormone robustly stimulated tyrosine phosphorylation and transcriptional activity of wild-type Stat5b while Stat5bA630P was minimally modified and did not promote reporter gene expression. Steady state levels of Stat5bWT were approximately 3-fold higher than Stat5bA630P in cell extracts prepared with nonionic detergents. Although initial rates of biosynthesis of both proteins were similar, pulse-chase experiments established that the apparent half-life of newly synthesized soluble Stat5bA630P was <15% of Stat5bWT (3.5 h versus >24 h). Stat5bA630P accumulated in cells primarily in cytoplasmic inclusion bodies. Structural analysis of the isolated SH2 domain containing the A630P mutation showed that it resembled the wild-type SH2 segment but that it exhibited reduced thermodynamic stability and slower folding kinetics, displayed an increased hydrophobic surface, and was prone to aggregation in solution. Our results are compatible with a model in which Stat5bA630P is an inactive transcription factor by virtue of its aberrant folding and diminished solubility triggered by a misfolded SH2 domain. The potential for aggregation and formation of cytoplasmic inclusions raises the possibility that Stat5bA630P could produce additional defects through inhibition of proteasome function.

Regulation of full-length and truncated growth hormone (GH) receptor by GH in tissues of lit/lit or bovine GH transgenic mice

Two truncated isoforms of growth hormone (GH) receptor (GHR) were identified in mice and in humans. The proteins encoded by these isoforms lack most of the intracellular domain of the GHR and inhibit GH action in a dominant negative fashion. We have quantified the mRNAs encoding the GHR isoforms in mouse tissues by use of real-time RT-PCR and examined the effect of GH excess or deficiency on regulation of mRNA levels of the GHR isoforms in vivo. In the liver, the truncated GHR mRNAs (mGHR-282 and mGHR-280) were 0.5 and <0.1%, respectively, the level of full-length GHR (mGHR-fl). In skeletal muscle, the values were 2-3 and 0.1-0.5% of mGHR-fl, respectively, and in subcutaneous fat, the values were 3-5 and 0.1-0.5% of mGHR-fl, respectively. The bovine GH transgenic mice showed a significant increase of mGHR-fl in liver but a significant decrease in skeletal muscle, with no difference in subcutaneous fat when compared with control mice. The lit/lit mice showed a significant decrease of mGHR-fl in liver, no difference of mGHR-fl in muscle, and a significant increase of mGHR-fl in subcutaneous fat when compared with lit/+ mice. The mRNA of mGHR-282 was regulated in parallel with mGHR-fl in all tissues of all mice examined, whereas that of mGHR-280 was not changed in either GH-excess or GH-deficient states. In conclusion, two truncated isoforms of GHR mRNAs were detected in liver, skeletal muscle, and subcutaneous fat of mice. The ratio of GHR-tr to GHR-fl mRNA was tissue specific and not affected by chronic excess or deficiency of GH.

Growth hormone receptor variant (L526I) modifies plasma HDL cholesterol phenotype in familial hypercholesterolemia: intra-familial association study in an eight-generation hyperlipidemic kindred

Defect of growth hormone receptor (GHR) is classically known to cause Laron syndrome, characterized by short stature, specific facial appearance, elevated serum growth hormone levels, and decreased insulin-like growth factor I levels. In addition, an increased cardiovascular risk due to elevated plasma total and LDL cholesterol levels marks another feature of the disease. Growth hormone (GH) plays an important role in the regulation of lipoprotein metabolism. GH status was found to be an independent determinant of plasma total cholesterol and triglyceride levels in humans. We studied a total of 207 members of eight-generation extended family of familial hypercholesterolemia (FH) in which affected members presented with various lipoprotein phenotypes. Intra-familial correlation analysis of a modifier effect of a Leu526Ile substitution in GHR gene was carried out among 95 carriers for LDL receptor gene (LDLR) mutation and 112 non-carriers. When plasma high-density lipoprotein cholesterol (HDL-c) levels in the LDLR-mutation carriers were compared, a significant lowering effect of HDL-c was observed with the Leu allele; the values were lowest among Leu/Leu homozygotes (mean +/- SD = 37 +/- 2 mg/dl), highest in Ile/Ile homozygotes (50 +/- 4 mg/dl), and intermediate among Leu/Ile heterozygotes (41 +/- 2 mg/dl) (P = 0.0021). The results indicate a significant modification of the phenotype of FH with the defective LDLR allele, by GHR Leu variation in the kindred studied.

Association of single nucleotide polymorphisms in the growth hormone and growth hormone receptor genes with blood serum insulin-like growth factor I concentration and growth traits in Angus cattle

This study was conducted to identify polymorphisms in the promoter and coding regions of the bovine growth hormone and growth hormone receptor genes and to study association of polymorphisms identified in these genes with growth traits and serum insulin-like growth factor-I (IGF-I) concentration. The denaturing gradient gel electrophoresis method and sequencing were utilized to identify three new single nucleotide polymorphisms in the promoter region of the growth hormone gene in Angus cattle. Polymerase chain reaction-based restriction fragment length polymorphism procedures were developed for rapid determination of the single nucleotide polymorphism genotypes in the growth hormone and the growth hormone receptor genes among Angus calves from lines divergently selected for high or low blood serum IGF-I concentration. The IGF-I concentration and growth traits were analyzed using animal models. The single nucleotide polymorphism in the promoter region of the growth hormone receptor gene was associated with serum IGF-I concentration on d 42 of the postweaning test and with mean IGF-I concentration. The associated effects of the markers need to be verified in other populations.

A novel heterozygous T51I mutation of growth hormone receptor is not associated with short stature

A novel missense mutation of the growth hormone receptor (GHR) gene was identified in a Japanese short boy with GH insensitivity. The analysis of the GHR gene revealed a novel heterozygous T51I mutation in exon 4. To clarify the effect of this mutation on GH signaling, the mutant GHR was expressed in CHO cells and its functional properties were investigated. The signal transducer and activator of transcription 5 (STAT5)-mediated transcriptional activation in mutant GHR (GHR-T51I)-expressing cells was significantly reduced as compared with wild-type GHR (GHR-wt)-expressing cells. The CHO cells co-expressing the GHR-T51I and GHR-wt, however, revealed no functional differences as compared with cells expressing GHR-wt alone, indicating that the T51I mutation does not exert the dominant negative effect. In addition, the mother and the elder brother of the proband, whose heights were normal, possessed the same heterozygous mutation. These results suggest that the heterozygous T51I mutation of GHR does not inhibit the signal transduction of GH and is not responsible for GH insensitivity.

The spectrum of hypopituitarism caused by PROP1 mutations

Mutations in the PROP1 gene are responsible for a high proportion of cases of multiple or combined anterior pituitary hormone deficiencies in humans. The physical and hormonal phenotypes of affected individuals are not uniform. The diagnosis is seldom considered during the first year of life. Growth failure is usually evident later in childhood. Deficiency of growth hormone (GH) tends to precede deficiency of thyroid-stimulating hormone (TSH). While most affected individuals fail to enter puberty without sex hormone replacement, some enter puberty but then develop pubertal arrest with a loss of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) responses to GnRH. Partial deficiency of corticotrophin (ACTH) is a late finding. Imaging of the pituitary may disclose either a small anterior pituitary gland or an intrapituitary mass. The mechanisms responsible for delayed loss of hormone production and the occasional overgrowth of the pituitary represent important areas for future research.

Skin fibroblasts of children with idiopathic short stature show an increased mitogenic response to IGF-I and secrete more IGFBP-3

OBJECTIVE AND PATIENTS

To study differences in cellular parameters of GH and IGF-I responsiveness in skin fibroblasts of 14 children with idiopathic short stature (ISS) treated with recombinant human GH and 13 children with normal height. Secondly, to investigate whether these cellular parameters can predict the growth response to GH treatment in children with ISS.

DESIGN AND MEASUREMENTS

The mitogenic responsiveness to GH and IGF-I was investigated by 3H-Thymidine incorporation. Insulin-like growth factor binding protein-3 (IGFBP-3) levels in the media were measured by radioimmunoassay (RIA).

RESULTS

No significant mitogenic responses were observed to various doses of GH (1000, 5000 or 50.000 ng/ml) in children with ISS or controls. ISS fibroblasts showed an increased mitogenic response to IGF-I (10 ng/ml) compared to controls (mean +/- SD 5.9 +/- 2.4- vs. 4.2 +/- 1.5-fold stimulation, P < 0.05), and GH enhanced this effect in both groups. IGFBP-3 secretion was increased in ISS fibroblasts when compared to controls under all conditions examined (basal, 200 and 5000 ng/ml GH, 10 ng/ml IGF-I for 24 and 48 h). High IGFBP-3 levels were related to low mitogenic responses to IGF-I or to GH + IGF-I in children with ISS (r = -0.7, P < 0.05), but not in controls. Within the ISS group, an enhanced mitogenic response to IGF-I in vitro was related to more extreme short stature before GH treatment (r = -0.70, P < 0.05) and to a relatively impaired response to high dose GH treatment in vivo (r = -0.52, P < 0.05).

CONCLUSION

The demonstration of high IGFBP-3 levels and enhanced mitogenic response to IGF-I shows that ISS fibroblasts have different cellular characteristics compared to controls of normal height. It is hypothesized that in ISS an alteration of the signal transduction pathway between the GH receptor and IGFBP-3 synthesis results in a local imbalance with high IGFBP-3 levels and lower IGF-I availability for the IGF-I receptor. This may be reflected by an increased IGF-I responsiveness in vitro which is associated with an impaired capacity to grow in vivo.

The C422F mutation of the growth hormone receptor gene is not responsible for short stature

A missense mutation, C422F, was identified in the intracellular domain of GH receptor (GHR) in a Japanese short boy. Although this mutation was previously reported in a patient with GH insensitivity syndrome (GHIS), it has not been clear whether this mutation causes GH insensitivity. To clarify the effect of this mutation on GH signal transduction, mutant GHR was expressed in CHO cells, and its functional properties were investigated. There were no significant differences in GH-induced tyrosine phosphorylation of STAT5b (signal transducer and activator of transcription) between wild-type GHR (GHR-wt)- and mutant GHR (GHR-C422F)-expressing cells. Moreover, STAT5-mediated transcriptional activation of GHR-C422F-expressing cells was comparable to that of GHR-wt-expressing cells. These findings indicated that the C422F mutation of GHR affected neither GH-induced tyrosine phosphorylation nor the transcriptional activation of STAT5. In addition, the analysis of genotypes and phenotypes of his family revealed that body heights of family members with heterozygous or homozygous C422F mutations were all within normal ranges, with the single exception of the proband. These in vitro and in vivo results indicate that the C422F missense mutation of GHR is a polymorphism that does not result in GHIS.

Natural history of growth hormone receptor deficiency

This review discusses the natural history of growth hormone receptor deficiency (GHRD) in relation to epidemiology, mortality, growth, certain aspects of body composition, and intellectual development. The majority of affected individuals are of Semitic origin and 90% come from the Indian peninsula, the Middle East, or elsewhere in the Mediterranean. There is a twofold increased mortality before the age of 7 years for children with GHRD. Affected adults may have increased cardiovascular risk resulting from increased total cholesterol and low-density lipoprotein cholesterol, unrelated to adiposity or insulin resistance. Intrauterine growth is affected minimally, if at all. Within a genetically homogeneous population in Ecuador, postnatal growth effects are as variable as in a large genetically heterogeneous population. There is no influence of parental heights. Areal bone mineral density is reduced in adults with GHRD, but estimated volumetric bone density (bone mineral apparent density) is normal. Intellectual development is unaffected by GHRD.

Serum levels of insulin-like growth factor binding proteins in Ecuadorean children with growth hormone insensitivity

Although insulin-like growth factor binding proteins (IGFBPs) are known to be important modulators of the action of insulin-like growth factors (IGFs), regulation of their production in vivo is not completely understood. Serum concentrations of IGFBP-3, -4 and -5 and acid-labile subunit (ALS) were therefore examined in 20 children with growth hormone (GH) insensitivity before and after 6 months of therapy with recombinant human IGF-I (80 or 120 micrograms/kg twice daily). The IGFBP concentrations in these children were compared with those in 62 GH-deficient children receiving GH therapy for 3 months. Serum levels of IGFBP-3, -4 and -5 and ALS all increased significantly (p < 0.0001) in GH-deficient children in response to GH therapy, whereas no significant increases occurred in the children with GH insensitivity. These findings indicate that GH is responsible for the regulation of serum levels of IGFBP-3, -4 and -5 and ALS, and that IGF-I does not directly regulate the concentrations of these circulating IGFBPs.

Short-term increments of insulin-like growth factor I (IGF-I) and IGF-binding protein-3 predict the growth response to growth hormone (GH) therapy in GH-sensitive children

The present study included a cohort of 42 children aged between 1.7 and 15.4 years, who presented with short stature and growth failure. Basal and generated serum levels of insulin-like growth factor-I (IGF-I) and IGF-binding protein-3 (IGFBP-3), measured in an IGF generation test following four or seven daily injections of growth hormone (GH), 0.1 IU/kg (0.033 mg/kg), were analysed in these patients. The growth response to 1 year of GH treatment, 0.6 IU/kg/week (0.2 mg/kg/week), was also investigated. Median height velocity of these patients increased from -1.6 SDS (range, -4.6 to -0.3 SDS) to 3.3 SDS (range, -0.2 to 7.1 SDS) after 1 year of GH treatment, and median height SDS increased by 0.7 SDS (range, 0.1 to 2.2 SDS). Strong correlations were observed between basal and generated IGF-I and IGFBP-3 levels. The increase in IGFBP-3 levels in response to GH in the generation test was a strong predictor of the growth response to GH therapy. All the patients in the present study could be differentiated from patients with GH insensitivity syndrome (GHIS) using the criteria of a diagnostic scoring system for GHIS. The most valuable parameters were the increases in IGF-I and IGFBP-3 levels in the generation test, which excluded 95.2% of the patients from a diagnosis of GHIS.

Lessons from the genetics of laron syndrome

In the decade since the cloning and sequencing of the growth hormone receptor (GHR) and the recognition that the circulating GH-binding protein (GHBP) is structurally identical to the extracellular domain of the GHR, 34 mutations have been described. These include one deletion, eight nonsense mutations, eleven missense mutations, four frameshift mutations and ten splice mutations. More than half of the 131 patients with Laron syndrome whose molecular defects have been identified comprise the Ecuadorian cohort who share a single splice mutation. Variable expression of different homozygous or compound heterozygous defects of the GHR is no greater than the variation within a genetically homogeneous population. Some features, such as birth size and intelligence, are unlikely to be affected by GHRD. Greater understanding of the genetics, physiology, and clinical expression of abnormalities in the GH-GHR-IGF-I (insulin-like growth factor I) axis necessitates a reconsideration of the classification of GH insensitivity (GHI).

The broad spectrum of inherited growth hormone insensitivity syndrome

Growth hormone (GH) insensitivity syndrome (GHIS) results in severe short stature and metabolic disturbances, but when this disorder is studied in more detail it is clear that there is marked clinical and biochemical heterogeneity. Many genetic defects of the GH receptor have been reported in inherited GHIS, but it now seems likely that some cases might be the result of defects of other genes or of links in the post-receptor cascade.

Stature in Ecuadorians heterozygous for growth hormone receptor gene E180 splice mutation does not differ from that of homozygous normal relatives

Heterozygosity for certain mutations of the GH receptor (GHR) gene has been proposed as the cause of partial resistance to GH, and there has been a recent demonstration of a dominant-negative effect of such a mutation in a mother and child. To examine the effect of heterozygosity in a large genetically homogeneous population with GHR deficiency, in which a substantial number of heterozygous (carrier) subjects and homozygous normal individuals can be compared, we studied a population in Ecuador in which 70 individuals with GHR deficiency were homozygous for the E180 splice mutation. We found that 58 heterozygous relatives of probands were not significantly shorter than 37 homozygous normal relatives [SD score (SDS) for height -1.85 +/- 1.04 (SD) vs. -1.55 +/- 0.96, P > 0.10]. When only those families with both homozygous normals and carriers were compared, the 33 heterozygous and 29 normal relatives did not differ significantly in height SDS (-1.98 +/- 1.07 vs. -1.77 +/- 0.91, P > 0.3). If heterozygosity for the E180 splice mutation were to influence stature, heights of heterozygous parents of probands would be expected to correlate with those of probands and of carriers who are their offspring and not with heights of their homozygous normal children. Parental height SDS did not correlate with height SDS of affected offspring (r = 0.24). For unaffected siblings as a group or analyzed separately as normals or carriers, there was a strong correlation between parental and offspring SDS for height (P < 0.01 for all comparisons). Thus, the effect of homozygosity for the GHR mutation was so profound as to abolish parental influence on height, and there was no difference in the influence of parental stature between carrier and noncarrier offspring. These findings demonstrate no meaningful effect on stature of heterozygosity for the E180 splice mutation of the GHR, which is a functional null mutation and, in the homozygous state, results in profound short stature from severe insulin-like growth factor-I deficiency.