IGF-I Generation Research Articles

Novel application of IGF-I and IGFBP-3 generation tests in the diagnosis of growth hormone axis disturbances in children with beta-thalassaemia.

Children with beta-thalassaemia major (beta-thal) frequently have growth retardation in the presence of low serum IGF-I and a normal GH response to pharmacological stimulation suggesting that they have GH insensitivity (GHIS). This study was carried out to study the cause of their growth retardation. We studied IGF-I and IGFBP-3 generation after exogenous GH administration for four days, in 15 prepubertal controls (C) and 41 prepubertal beta-thal patients divided into three groups according to their growth status: (Group 1) 15 with normal growth (N-thal) (Group 2) 16 with decelerated growth (D-thal) and (Group 3) 10 with short stature (S-thal), in order to determine whether GHIS is the cause of their growth retardation. IGF-I and IGFBP-3 were measured daily, before and for 4 days after daily administration of 0.1 IU/kg hGH, in 3 groups of prepubertal beta-thal patients and normal controls. N-thal and C had similar basal serum IGF-I (142 +/- 52 and 196 +/- 56 ng/ml, respectively) and IGFBP-3 concentrations (2.07 +/- 0.49 and 2.66 +/- 0.41 mg/l, respectively) as well as a similar percent increase of IGF-I (101 +/- 23% and 104 +/- 37%, respectively) and IGFBP-3 (52 +/- 36%, and 38 +/- 14%, respectively) during the generation tests. S-thal and D-thal had significantly lower basal IGF-I and IGFBP-3 concentrations (85 +/- 42 and 101 +/- 36 ng/ml; and 1.60 +/- 0.49 and 1.79 +/- 0.52 mg/l, respectively) as compared to N-thal and C (P < 0.001 and P < 0.005, respectively), and a significantly higher percent increase of IGF-I and IGFBP-3 during the generation tests (249 +/- 43 and 161 +/- 76%; and 121 +/- 99 and 73 +/- 35%, respectively) as compared to N-thal and C (P < 0.0001 and P < 0.01, respectively). Twenty-five percent of the growth retarded patients had classic GH deficiency (GHD) and percent increases of IGF-I and IGFBP-3 in the generation tests (164 +/- 86% and 80 +/- 49%, respectively) which were similar to those of the remaining growth-retarded children. The greater percent increases of IGF-I and IGFBP-3 in the generation tests of the growth retarded beta-thal patients, both with and without GHD, strongly suggest impaired GH secretion rather than GHIS as the cause of their growth retardation. We conclude that the IGF-I and IGFBP-3 generation tests are useful tools for the study not only of GHIS but also of GH secretory disorders in patients with beta-thal and short stature that can easily be performed in an outpatient setting as an initial test to identify the patients that may benefit from GH therapy.

Clinical and Endocrine Characteristics in Atypical and Classical Growth Hormone Insensitivity Syndrome

Objective: Classical growth hormone insensitivity syndrome (GHIS) comprises a dysmorphic phenotype, extreme short stature (height SDS < 3), normal GH and low IGF-I and IGFBP-3. Wide clinical variation is recognised with classical and atypical forms. We aimed to delineate features of the milder ‘atypical’ GHIS phenotype, and to determine whether this correlates with milder auxological and biochemical features. Methods: Fifty-nine patients from a European series of 82 patients with GHIS, with strict diagnostic criteria of GHIS, were studied and assigned to classical or atypical GHIS groups according to facial phenotype, i.e. ‘classical’ required 2 of 3 recognized GHIS features (frontal bossing, mid-facial hypoplasia and depressed nasal bridge), ‘atypical’ required 0 or 1 of these facial features. Classical and atypical GHIS groups were compared in terms of (1) phenotypic features, including high-pitched voice, sparse hair, blue sclera, hypoglycaemia, microphallus, (2) birth length, height SDS, and (3) basal IGF-I, IGF-II, IGFBP-1, IGFBP-3, GHBP and increase in IGF-I on IGF-I generation testing. Results: Fifty patients [24 males, 26 females, aged 8.6 ± 4.6 years (mean ± SD)] had ‘classical GHIS’, 9 patients (7 males, 2 females, aged 7.8 ± 4.1 years) had ‘atypical GHIS’, 7 with normal facies. Atypical GHIS patients had lesser height deficit (Ht SDS –4.0 ± 1.4) compared to classical GHIS (–6.7 ± 1.4), less reduction in IGFBP-3 SDS (atypical –5.5 ± 3.3; classical –8.6 ± 2.4), and more had normal GHBP (>10% binding). Other variables were also less frequent in atypical GHIS patients: high-pitched voice 11% (70% classical), sparse hair 11% (42% classical), blue sclera 0% (38% classical), hypoglycaemia 11% (42% classical), and microphallus 14% (1 of 7 males), compared to 79% of classical (19 of 24 males). Conclusions: Atypical GHIS patients, with relatively normal facial appearance, demonstrate less height defect and biochemical abnormalities compared to classical patients. GH insensitivity may be present in children with short stature and an otherwise normal appearance.

The GH/IGF-I axis in obesity: influence of neuro-endocrine and metabolic factors.

In this review we propose an integrated neuro-endocrine-metabolic point of view on the alterations (adaptations?) of GH/IGF-1 axis in obesity, summarizing the evidence from the literature, particularly focusing the data on humans and adding where possible results from our studies in this field. It is well-known that GH secretion is deeply impaired in overweight patients: we reviewed the multiple mechanisms underlying this issue, considering either central (CNS-related, such as impairment of GHRH tone or increased somatostatin release) or peripheral (ie metabolic: insulin, free fatty acids, glucose) factors. A central point of the debate about GH insufficiency in obesity is if it represents a simple adaptive phenomenon or reflects a true impairment of the axis activity. Evaluation of IGF-I levels and generation in obesity was the mean used to address this question: a bulk of evidence on IGF-I balance in human obesity has been provided, but the matter is still uncertain and unsolved.

Study of growth hormone secretion and action in growth-retarded children with juvenile chronic arthritis (JCA).

The stimulated and spontaneous growth hormone (GH) secretion and the response to GH action were assessed in growth-retarded children with juvenile chronic arthritis (JCA), in order to determine the underlying mechanisms of growth retardation in such children. Six children (4 boys and 2 girls aged 10.7-13.8 years) with active JCA of systemic onset were included in the study which involved: (1) anthropometric measurements; (2) assessment of GH responses to insulin-induced hypoglycaemia and clonidine stimulation; (3) assessment of the nocturnal pulsatile GH secretion by measuring GH in blood samples obtained every 20 min from 20.00 to 08.00 h; and (4) the IGF-I generation test. As a control, the latter test was also performed in eight aged-matched children with physiological delay in puberty. Biosynthetic hGH (0.1 IU/kg BW) was administered s. c. for 4 days and blood samples were taken at baseline and the morning after the last GH injection for measurement of IGF-I and IGFBP-3. All six children with JCA were prepubertal and their growth velocity was <3 cm/year. The GH responses to both stimulation tests were normal (peak GH >20 mU/l). Analysis of the pulsatile GH secretion during the night revealed three-to-four GH pulses of normal amplitude (>20 mU/l). IGF-I (26.7+/-4.6 nmol/l, mean+/-SD) and IGFBP-3 (2.1+/-0.2 mg/l) levels were lower in the patients compared with the controls (43.0+/-3.7 nmol/l and 2.8+/-0.2 mg/l, respectively, P<0.01). Following stimulation with exogenous hGH, there was a significant increase in IGF-I and IGFBP-3 levels in the control group (85 and 73%, respectively), but only a small increase in the patients (31 and 14%). It appears that stimulated and spontaneous GH secretion is normal in children with active systemic JCA, but the response to endogenous and exogenous GH with regard to IGF-I and IGFBP-3 production is impaired, indicating a degree of GH insensitivity in such children.

Growth hormone-insulin-like growth factor-I axis in adult insulin-dependent diabetic patients: evidence for central hypersensitivity to growth hormone-releasing hormone and peripheral resistance to growth hormone.

The aim of this study was to assess the GH-IGFI axis, GH receptor availability, as reflected by the levels of GH-BP, and the amount of GH-dependent IGFBP-3 in adult IDDM patients with different degrees of metabolic control. Thus, 10 adult well-controlled IDDMs (HbA1 7.8 +/- 0.4%), 10 adult non-ketotic poorly controlled IDDMs (HbA1 13.3 +/- 7%) and 14 sex- and age-matched healthy controls were subjected to two intravenous GH-RH stimulation tests with 0.1 and 1.0 microg/kg body weight respectively, and a plasma IGF-1 generation test induced by the administration of hGH. Poorly controlled IDDM patients exhibited an exaggerated GH response to 1.0 microg/kg of GH-RH when compared to healthy control subjects. Low fasting plasma IGF-1 levels and a blunted IGF-1 response to exogenously administered hGH were also found in poorly controlled IDDMs when compared to the healthy control group. GH-BP levels were significantly lower in IDDMs than in normal controls, and correlated positively with the IGF-1 generation capacity after hGH. Serum IGFBP-3 levels measured by RIA were similar in IDDM and control groups. Good glycemic control for 5.7 +/- 0.9 months did not correct the above mentioned abnormalities of the GH-IGF-1 axis. Our findings suggest that IDDM is associated with a diminished availability of GH receptors and synthesis of IGF-1. GH might then increase as a compensatory mechanism, further down-regulating liver GH receptors, and thus perpetuating the initial abnormality.

IGF-I generation test: Effects on body composition

IGF-I generation test: Effects on body composition

Changes in serum IGF-I and IGFBP-3 concentrations during the IGF-I generation test performed prospectively in children with short stature.

Genotype and phenotype heterogeneity in patients with GH insensitivity syndrome suggests that partial defects exist in the GH receptor. Children with partial GH resistance would be expected to have short stature, elevated GH levels and relatively low levels of IGF-I and IGFBP-3. Provocation tests of the GH-IGF-I axis may help to identify such children. The IGF-I generation test in particular may demonstrate impaired secretion of IGF-I and IGFBP-3. This prospective study assesses the usefulness of the IGF-I generation test in the identification of short children with possible GH insensitivity. Prepubertal children referred for assessment of short stature underwent a standard GH provocation test followed by an IGF-I generation test. Thirty-seven prepubertal children (14 girls, 23 boys) with short stature (height < 2nd centile UK standards 1990) aged 4.5-12.6 years were investigated prospectively. Assessment included history, physical examination, auxological observations (height, weight, bone age). GH provocation tests (glucagon 15 micrograms/kg i.m. or insulin 0.15 U/kg/i.v.) was followed by an IGF-I generation test (hGH 0.1 iu/kg/s.c. daily for 4 days). GH was assayed during the provocation test. IGF-I and IGFBP-3 were measured at 0900 h on day 0 and 4 of the IGF-I generation test. GH and IGF-I were measured by radioimmunoassay, IGFBP-3 by IRMA and basal GHBP by HPLC. Height SDS was calculated according to the UK Height Standards 1990. The absolute and percentage changes of IGF-I and IGFBP-3 during the IGF-I generation test were calculated. The 37 children were divided into three groups according to the peak GH level (mean +/- SEM) during the provocation test: Group 1 (peak GH < 20 mU/l) n = 11, five girls, six boys age 7.1 +/- 0.7 years, height SDS -2.5 +/- 0.1, peak GH 14.5 +/- 1.6 mU/l, IGF-I 92.0 +/- 10.4 micrograms/l, IGFBP-3 2.6 +/- 0.4 mg/l. Group 2 (peak GH 20-40 mU/l) n = 12, six girls, six boys age 8.6 +/- 0.7 years, height SDS -2.6 +/- 0.1, peak GH 28.4 +/- 1.6 mU/l, IGF-I 121-5 +/- 13.4 micrograms/l, IGFBP-3 2.9 +/- 0.2 mg/l. Group 3 (peak GH > 40 mU/l) n = 14, three girls, 11 boys, aged 8.5 +/- 0.6 years, height SDS -2.3 +/- 0.1, peak GH 60.7 +/- 4.1 mU/l, IGF-I 112.4 +/- 10.9 micrograms/l, IGFBP-3 3.1 +/- 0.3 mg/l. There were no significant differences in the absolute increases of IGF-I or IGFBP-3 (mean +/- SEM) during the IGF-I generation test, IGF-I; Group 1, 48.8 +/- 9.5 micrograms/l, Group 2, 42.7 +/- 4.8 micrograms/l. Group 3, 45.5 +/- 5.1 micrograms/l, IGFBP-3; Group 1, 1.1 +/- 1.2 mg/l. Group 2, 1.2 +/- 0.2 mg/l, Group 3, 0.85 +/- 0.1 mg/l. There were no significant differences in the percentage increases (mean +/- SEM) of IGF-I; Group 1, 55 +/- 9%, Group 2, 35 +/- 5%, Group 3, 42 +/- 8%, or IGFBP-3; Group 1, 64 +/- 17%, Group 2, 44 +/- 8%, Group 3.32 +/- 6%. GHBP values were normal in all three groups. In Group 3 (peak GH > 40 mU/l) four individual patients had either low basal IGF-I levels (n = 2) (< 5th centile of normal range for age) or low basal IGFBP-3 levels (n = 1) (< 5th centile of normal range for age) or low IGF-I responses in the IGF-I generation test (2 x CV of IGF-I assay) (n = 1). No single subject had all the characteristics of GH insensitivity syndrome. The responses during an IGF-I generation test did not identify a clear group of children with GH insensitivity. Individual patients had low basal IGF-I or IGFBP-3 values and a poor response in the generation test, features which, in the presence of high GH levels on provocation, are consistent with partial GH insensitivity.

Heterozygous mutation in the WSXWS equivalent motif of the growth hormone receptor in a child with poor response to growth hormone therapy

Besides complete GH insensitivity syndrome (GHIS) described by Laron, clinical and molecular evidences have accumulated concerning partial GHIS. We studied GH receptor (GHR) gene in children who show poor response to GH treatment and detected a patient with a heterozygous mutation in exon 7 leading to the Y222H substitution. This missense mutation, located in the YGEFS motif of the GHR equivalent to the WSXWS motif highly conserved throughout all members of the cytokine receptor family, has not been described so far. Although we cannot conclude on the deleterious effect of this mutation, there are several lines of evidence suggesting that it could account for the partial GH insensitivity: (i) hormonal data including IGF-I generation test; (ii) molecular data - no other mutation was identified in the coding sequence, the father who has the same mutation is short, the brother did not inherit the mutated allele and was of normal height.

Additive Effects of GH and Testosterone on the Anabolic Changes of Puberty: A Metabolic Study † 459

During human puberty there is a dramatic rise in GH sex steroids concentrations and in GH production rates and IGF-1. These studies were designed to investigate the relative contributions of testosterone (T) and GH on the metabolic changes of puberty. 6 boys with GH deficiency (defined as profound growth retardation (>-2.5 Height SDS), poor growth velocity and peak GH responses to secretagogues <7ng/ml) were studied (mean age: 12±0.7 yrs). Mean bone age at entry was: 10.4±0.8 yrs. After a weight maintenance diet for 3d prior to admission, patients were admitted to the Research Unit. The next a.m., after an overnight fast, whole body protein kinetics were studied using a stable isotope of leucine (13C-leu) for 4 hrs and frequent blood, breath and urine samples obtained as well as indirect calorimetry. Body composition was measured by Bioelectrical Impedance Analysis(BIA), calipers and DEXA scan. After the baseline study (D1), the boys were begun on T enanthate, 50-75mg IM, dose repeated in 3w, and the study repeated identically within 4w of D1 (D2). After D2, the boys were begun on daily SQ injections of rhGH (Nutropin, Genentech) at 0.3mg/kg.w while T Rx was continued. After another 4w, studies were repeated a 3rd time(D3), each subject as their own control. Four patients have completed these studies thus far. Fat free mass (FFM) by BIA increased after T Rx (+5%), and +12% after T/GH Rx (p=0.002 vs D1), with a concomitant decrease in%FM after T Rx (-11%), with an even greater decline as compared to baseline on D3 (-25%, p=0.03). Rates of whole body proteolysis (Leucine Ra) did not change after T Rx (+2%) and increased +18% after T/GH Rx (p=0.08); leucine oxidation decreased on D2 (-28%, p=0.06), and declined even further after D3(-36%, p=0.02); and non-oxidative leucine disposal, a measure of protein synthesis, increased modestly on D2 (+10%), and +32% on D3 (p=0.03). These changes paralleled the decrease in protein oxidation rates on D2 (-31%, p=0.05), and even greater decline on D3 (-41%, p=0.014). Plasma IGF-1 concentrations increased significantly after T Rx (+70%) and even more after T/GH Rx (+182%, p=0.03). In summary: T and GH appear to have additive effects on body composition, protein anabolism and IGF-1 generation. In conclusion: Preliminary studies suggest that GH and T can independently affect body composition in males.

Growth hormone-stimulated insulin-like growth factor (IGF) I and IGF-binding protein-3 in liver cirrhosis

Background/Aims: The aim of this study was to evaluate the liver's potential to generate insulin-like growth factor (IGF) I and IGF-binding protein-3 (IGFBP-3), following stimulation by human recombinant growth hormone, as a possible marker for liver functional reserve in patients with liver cirrhosis. Methods: In a pilot study, 15 patients (mean age 56 years) with postnecrotic liver cirrhosis were divided into two groups according to disease severity (ChildPugh score): Group 1 ( n=8) with scores of 5–8 and Group 2 ( n=7) with scores of 9–12. Five age-matched healthy subjects served as controls. Human recombinant growth hormone (0.06 mg/kg) was administered subcutaneously on 2 consecutive days. Serum levels of IGF-I and IGFBP-3 were measured before and up to 48 h after human recombinant growth hormone injection. Nutritional status was assessed by the creatinine-height index and was compared to lymphocyte count, body mass index, and muscle arm circumference. Results: Baseline IGF-I levels were significantly lower in patients with cirrhosis than in controls, while no differences were not between the two patients groups. IGF-I levels increased significantly after rhGH administration to the healthy controls, to a lower degree in Group 1, while no change occurred in Group 2. IGF-I levels at 24 h and beyond correlated significantly with the nutritional status, the Child-Pugh score, and the basal levels of GH-binding protein and IGFBP-3. IGFBP-3 serum levels did not change after rhGH stimulation. Conclusions: IGF-I generation after GH stimulation may provide a new dimension in the assessment of liver function and nutritional status in patients with liver cirrhosis.

Short stature and failure of pubertal development in thalassaemia major: evidence for hypothalamic neurosecretory dysfunction of growth hormone secretion and defective pituitary gonadotropin secretion.

In patients with beta-thalassaemia major, frequent blood transfusions combined with desferrioxamine chelation therapy lead to an improved rate of survival. Endocrine disorders related to secondary haemosiderosis such as short stature, delayed puberty and hypogonadism are major problems in both adolescent and adult patients. A total of 32 patients with beta-thalassaemia major undergoing treatment at the Children's Hospital, University of Göttingen were examined. Fourteen of these were short in stature. Growth hormone (GH) secretion was investigated in 13 patients exhibiting either a short stature or reduced growth rate. The stimulated GH secretion of 10 patients in this subgroup lay within the normal range. Studies of their spontaneous GH secretion during the night revealed that these patients had a markedly reduced mean GH and reduced amplitudes in their GH peaks. Low insulin-like growth factor (IGF)-I levels were seen in the growth-retarded thalassaemic patients. Eight were subjected to an IGF generation test and showed a strong increase in both IGF-I and insulin-like growth factor binding protein (IGFBP)-3 levels indicating intact IGF-I generation by the liver. Hypogonadotropic hypogonadism was found to be present in both the male and female patients with impaired sexual development. After priming with LH-releasing hormone (GnRH) per pump in 2 female and 5 male patients, no change in either their serum oestradiol or testosterone levels or in LH/FSH response to GnRH was observed suggesting that they were suffering from a severe pituitary gonadotropin insufficiency. Three male patients at the age of puberty but exhibiting short stature. low GH, low IGF-I and hypogonadism received low dose long-acting testosterone. After 3 12 months of therapy there was a marked growth spurt, higher nocturnal GH levels and an increase in both IGF-I and IGFBP-3. Reduced GH secretion and low IGF-I in thalassaemic patients are related to a neurosecretory dysfunction due to iron overload rather than to liver damage. Hypogonadotropic hypogonadism is caused by the selective loss of pituitary gonadotropin function. In patients with both GH deficiency and hypogonadism, low dose sexual steroid treatment should be considered either as an alternative or an additional treatment before starting GH therapy.

Growth deficiency in polytransfused beta-thalassaemia patients is not growth hormone dependent.

Growth deficiency is commonly seen in polytransfused beta-thalassaemia patients, especially in adolescence. It is not completely dependent on the lack of their pubertal growth spurt. GH impairment at different levels (hypothalamic or pituitary) and/or a reduced IGF-1 synthesis have been suggested the main causes of stunted growth in these patients. We evaluated the relationship between GH reserve and growth in short beta-thalassaemia patients. Twenty-nine short patients (height < -1.8 SDS for chronological age) were divided into two groups (low and normal responders) on the basis of their GH peak during insulin and clonidine tests (< or = and > 20 mU/l, respectively). All but one low responders underwent the GHRH test to exclude the impairment of somatotroph function and in eight of them an IGF-1 generation test was also performed. The two groups were compared with each other with respect to growth (height deficiency, height velocity, bone age and bone delay), haematological characteristics (serum ferritin levels, age at the start both of low (subcutaneous) s.c. infusion of desferrioxamine and of transfusional therapy) and serum IGF-1 and IGF-1 binding protein 3 levels. Thirteen patients (45%) (11 males, two females) were low responders, all but two having serum IGF-1 < 5th centile (< 0.1 centile in 42%); the GHRH test excluded the impairment of somatotroph function in 8/12. Height deficiency, serum ferritin levels, and age at the start of s.c. chelating therapy did not differ in low compared to normal responders. Height was negatively correlated both with the age at the start of s.c. chelating therapy and with serum ferritin levels. The reduction of GH reserve, more frequently due to a hypothalamic than to a pituitary dysfunction, is frequent in polytransfused beta-thalassaemia patients, especially in males. The height function is not related to the GH reserve, given the current methods for testing GH reserve. Late start of s.c. chelating therapy as well as haemosiderosis seem to play a role in the height deficiency, but not in GH reserve. Impairment of GH secretory reserve, therefore, cannot be considered the main cause of height deficiency in these patients.

The effects of octreotide on GH receptor and IGF-I expression in the GH-deficient rat

Somatostatin has been suggested to influence the somatotrophic axis outside the central nervous system, in reducing GH-induced IGF-I mRNA and IGF-I generation. This study aimed to determine whether such effects were mediated via the GH receptor (GHR). GH-deficient dwarf rats aged 45-47 days (n = 8 per group) received twice daily subcutaneous injections of octreotide (1 mg/kg) (group O), saline (group S), octreotide (1 mg/kg) plus bovine GH (0.25 mg/kg) (group OG), or bovine GH (0.25 mg/kg) plus saline (group G) for 10 days. Octreotide-treated animals had less weight gain compared with saline-treated animals, but not when GH cotreated (group OG vs G). Octreotide had an overall effect on decreasing length gain (P < 0.01). Serum IGF-I (ng/ml) was reduced by octreotide (group O 171 +/- 11, group S 239 +/- 20, P < 0.01; group OG 283 +/- 30, group G 362 +/- 10, P < 0.001), as was serum insulin (P < 0.001). A significant decrease in hepatic and muscle IGF-I mRNA expression was found as expected, yet this was not associated with decreased hepatic GHR expression. Rather, an increase in hepatic 125I-bovine GH specific binding was observed (P < 0.001) and, in GH-cotreated animals (OG), hepatic GHR and GH binding protein (GHBP) mRNA expression were also increased by octreotide by approximately 40%. In muscle, octreotide was associated with an approximately 30% decrease in GHBP mRNA and no effect on GHR mRNA. This study suggests that the suppressive effects of octreotide on IGF-I metabolism, at least in liver, are not mediated via down-regulation of GHR expression, but more likely by direct effects on IGF-I expression.

Insulin-Like Growth Factor Binding Protein-3 Generation: An Index of Growth Hormone Insensitivity

GH insensitivity may be an inherited condition or may arise as a consequence of disease of malnutrition. Laron syndrome is the most severe form of GH insensitivity, arising from an absent or defective GH receptor. Less severe forms of GH insensitivity, however, may exist, resulting in short stature but in few other features of Laron syndrome. We have identified a heterogeneous group of children with short stature and either high basal (> 10 mU/L) or high peak GH levels (> 40 mU/L) on GH provocation testing, to examine biochemical markers of GH sensitivity. These children received 4 d of GH (0.1 U/kg) and the increment in IGF-I, IGF binding protein (BP)-3, and GHBP was determined. Eight GHD children, commencing GH therapy, were recruited as positive controls. The two groups could not be differentiated by age, height SDS (SD score), height velocity SDS, or body mass index. IGF-I and IGFBP-3 generation were correlated in all children (delta SDS IGF-I versus delta SDS IGFBP-3, r = 0.49, p = 0.03). Neither basal GHBP levels or the increment in GHBP were predictive of the IGF-I or IGFBP-3 response to GH. The GHI group had a significantly reduced IGFBP-3 response to stimulation with 4 d of GH (median percent increment in IGFBP-3, 26%, versus 72% in the GHD group, P = 0.03); their IGF-I response to GH was also reduced (median % increment in IGF-I 75% versus 144% in the GH deficient group), but this did not achieve significance, p = 0.06. In all children, the percentage rise or delta SDS in both IGF-I and IGFBP-3 inversely correlated with the GH peak obtained on provocation testing, the latter being the most significant determinant of GH peak. We propose that the "IGF generation test", in particular IGFBP-3 generation, can be used in the investigation of partial GH insensitivity. Further work, however, is required to establish diagnostic criteria for partial GH insensitivity.

IGF-I Deficiency and Growth Failure: Association with Mutations in the Intracellular Domain of the Growth Hormone Receptor Gene. ▴ 541

Abnormalities of the extracellular domain of the growth hormone (GH) receptor gene have been identified as possible links to the short stature of certain children. Recently, we had the chance to investigate a young boy with profound growth retardation and a novel mutation in theintracellular domain of the GH receptor (GHR) gene. At 6 10/12 yrs he was evaluated for short stature (Ht:-4 SDS), despite normal weight (50% ht for wt curve). Bone age was 4 6/12 yrs. Parents' heights were normal (Mother:-0.3, Father: -0.1 SDS). Peak GH response to secretagogues was: 15.3 ng/mL; extracted IGF-I: 57 ng/mL (88-474); IGFBP3: 1.5 mg/L (0.9-4.1); GHBP: 156 pmoL/L (63-250). An IGF-I generation test performed (0.06 mg/kg·d for 5d) failed to raise his circulating IGF-I concentrations (68 ng/mL). WBC's from the patient and immediate family were transformed using EBV, and the GHR gene analyzed using PCR and single strand conformational polymorphism analysis(SSCA) of each of the coding exons. SSCA of exons 2 through 10 of the GHR gene revealed 4 aberrant bands for exon 10, which encodes for theintracellular domain of the GHR. The proband carried 2 single base pair changes: one, a silent base pair substitution in codon 473 (which encodes for serine); another in codon 478 (G to A) causing an amino acid substitution(ALATHR). His mother carried the 478Thr mutation, and the father the silent 473Ser mutation. A 4 year old sister (HT: -0.5 SDS) carried the wild type receptor, and a 6 year old sister (HT: -1.9 SDS) has an identical genotype as the proband. Since the patient is of hispanic (Puerto Rican) parents we extended the analysis to 10 Puerto Rican and 24 caucasian controls. Neither of these GHR changes were found in these 34 individuals.

Review of Turkish patients with growth hormone insensitivity (Laron type).

Clinical spectrum and endocrine details of thirteen Turkish children (age 0.3-14.2 years; eight females and five males; ten prepubertal, three pubertal) with growth hormone insensitivity are presented. All patients display phenotypical features of severe growth hormone deficiency. The diagnosis based on height standard deviation score (SDS), basal growth hormone (GH), basal insulin-like growth factor I (IGF-I, IGF-I response in an IGF generation test and growth hormone binding protein (GHBP) measurements. The median height SDS was -7.4 (range -3.2 to -10), weight for height index was 100 (range 81-152) and bone age/height age ratio was 2 (range 1.6-3.3). Endocrine investigations showed a median basal GH concentration of 61.4 mU/l (range 23.5-120 mU/l). Basal IGF-I level was below 10 ng/ml in all patients except one. None of the patients showed a significant IGF-I response to injections of GH (0.1 U/kg body weight for 4 days). The median IGFBP-3 level was 0.23 mg/l (range 0.1-0.56 mg/l). The GHBP level was undetectable in all of 10 patients. The high number of patients in our center may be due to the high rate of consanguinity among the Turkish population and the referral facility of our center in the area. These patients may benefit from the new therapy with recombinant human IGF-I.

Is IGF binding protein‐3 assessment helpful for the diagnosis of GH deficiency?

The measurement of serum immunoreactive IGFBP-3 levels has been proposed as a screening test to identify children with growth hormone deficiency (GHD). We tested the sensitivity and specificity of the IGFBP-3 assessment in comparison with the measurement of IGF-I. We assessed the IGFBP-3 and IGF-I circulating levels in normal subjects and patients with GHD or idiopathic short stature (ISS). Eighty-two normal subjects, 16 GHD, and 10 children with ISS were studied. Controls were divided into three age groups: group A, 1-4 years (n = 16); group B, 5-9 years (n = 35), and group C, 10-14 years (n = 31). All subjects underwent standard anthropometry. In short patients, GH secretory status was assessed by clonidine and arginine stimulation tests. IGFBP-3 and IGF-I circulating levels were measured by radioimmunoassay. IGFBP-3 and IGF-I levels were closely related (r = 0.51, P < 0.0001) and IGFBP-3 was less age dependent than IGF-I (r = 0.57, P < 0.02 vs r = 0.64, P = 0.0001). Sensitivity (true positive ratio) and specificity (true negative ratio) of IGFBP-3 measurement were 50 and 92% respectively, whereas sensitivity and specificity of IGF-I assessment were 75 and 90% respectively. Below the age of 5 years, sensitivity was 20% for IGFBP-3 and 40% for IGF-I; specificity was 94% for IGFBP-3 and 88% for IGF-I. IGFBP-3 measurement had poor sensitivity in detecting growth hormone deficient patients, offering no diagnostic advantage over IGF-I, even in the first years of life, although, due to the high specificity, the finding of subnormal levels of IGFBP-3 was strongly suggestive of growth hormone deficiency. The presence of low IGFBP-3 and IGF-I levels in a short child with normal GH response to provocative tests should prompt further investigations, such as the determination of spontaneous GH secretion or assessment of the GH binding proteins together with an IGF-I and/or IGFBP-3 generation test, in order to identify neurosecretory dysfunction or GH receptor deficiency. Finally, we believe that there is no definitive test for diagnosing or excluding growth hormone deficiency and detailed analysis of the results of endocrine tests, clinical findings and other laboratory and radiological information is necessary to maximize diagnostic accuracy.

Tissue-specific regulation of the growth hormone receptor gene in streptozocin-induced diabetes in the rat

Abnormalities of GH secretion and clearance are well-documented in poorly controlled insulin-dependent diabetes mellitus (IDDM), but the contribution of the receptor (GHR) and the GH-binding protein (GHBP) to these abnormalities has not been defined. We studied the expression of the GHR/GHBP gene in the livers, hearts and kidneys in streptozocin-induced diabetes (STZ-D) in the rat. GHR and GHBP mRNA levels were measured by Northern blot and ribonuclease protection assays. Whereas levels of GHR and GHBP mRNA were significantly decreased in liver and heart of STZ-D rats when compared with the control group (P < 0.01), GHR mRNA was significantly increased in the kidneys of STZ-D rats (P = 0.03). Six days of insulin treatment did not significantly alter the levels of GHR/GHBP mRNA in the liver or heart of STZ-D rats, but significantly decreased GHBP mRNA (P = 0.04) in the kidney. Circulating IGF-I was reduced, as was IGF-I mRNA in the liver and heart of STZ-D rats; only circulating IGF-I was restored by insulin treatment. Neither STZ-D nor insulin treatment affected IGF-I or IGF-I receptor mRNA concentrations in the kidney. We conclude that (1) STZ-D modulates the expression of the GHR/GHBP gene and (2) that these changes in GHR/GHBP mRNA concentrations are tissue-specific; STZ-D decreases GHR/GHBP mRNA in liver and heart tissue but increases GHR mRNA concentrations in the kidney. Our results indicate a role for decreased numbers of hepatic GHRs in the pathogenesis of resistance to GH's actions in terms of IGF-I generation and promotion of linear growth in IDDM. We postulate that increased GHR expression in the kidney may be involved in the renal complications of IDDM.

The insulin-like growth factor I generation test: resistance to growth hormone with aging and estrogen replacement therapy.

Circulating IGF-I is primarily regulated by growth hormone, but other factors such as nutritional status may also influence IGF-I secretion. The effects of age, gender, and estrogen replacement on responsiveness of serum IGF-I to GH administration have not been directly studied. The high-affinity circulating GH-binding protein (GHBP) has the same structure as the extracellular domain of the GH receptor and may reflect the sensitivity to GH in humans. To examine these issues, we employed an IGF-I generation test in which a single dose of GH (0.1 mg/kg SQ) was administered to 31 healthy adults comprising five groups: young (20-29 years) males (YM), young females in the follicular phase of the menstrual cycle (YF), older (60-69 years) males (OM), older females not on estrogen replacement (OFN), and older females on oral estrogen replacement (OFE). Blood was sampled for IGF-I and GHBP over 72 hours following GH administration. OM had lower peak IGF-I levels (323 +/- 38 vs. 497 +/- 85 micrograms/l, p = 0.0015) and a lower IGF-I response to GH (delta IGF-I: 187 +/- 33 vs. 293 +/- 57 micrograms/l, p = 0.0085) than YM. OFE had lower basal IGF-I (63 +/- 11 vs. 133 +/- 19 micrograms/l, p = 0.0046), peak IGF-I (174 +/- 28 vs. 400 +/- 40 micrograms/l, p = 0.0015), and delta IGF-I (111 +/- 21 vs. 268 +/- 27 micrograms/l, p = 0.0085) than OFN. IGFBP-3 levels were unchanged 24 hours after GH administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Improvement of diagnostic criteria in growth hormone insensitivity syndrome: solutions and pitfalls

A survey to identify children and adolescents with primary growth hormone insensitivity syndrome (GHIS) yielded 38 patients who were positively identified using a scoring system that included five criteria: height, basal growth hormone (GH), GH binding protein, basal insulin-like growth factor I (IGF-I) and the increase of IGF-I after 4 days of GH administration (IGF generation test). Because of an overlap of the accepted and excluded groups with respect to points scored, an attempt was made to improve the scoring system. The new criteria were: height below -3 SDS, basal GH 4 mU/l or above, GH binding below 10%, basal IGF-I and basal IGF binding protein-3 (IGFBP-3) below the 0.1 centile for age, an increase of IGF-I in the IGF generation test less than 15 micrograms/l, and the increase of IGFBP-3 less than 0.4 mg/l. With this scoring system, a clear separation between the accepted and the excluded groups was obtained. IGFBP-3 was included to give the GH-dependent parameters of the IGF system more weight and because the accuracy of IGFBP-3 in the IGF generation tests was greater than the accuracy of IGF-I, when the group of patients with GHIS was compared with a group of patients with GH deficiency. Unexpectedly, the IGF generation test was unable to segregate both cohorts completely. In the GHIS-positive group, a significant correlation was found between basal IGF-I or IGFBP-3 levels corrected for age (SDS) and height SDS (r = 0.49, p < 0.002 and r = 0.61, p < 0.0001, respectively). There was also a significant correlation between the changes of IGF-I or IGFBP-3 in the IGF generation test and height SDS. That is, the patients with a slight response to GH were those with the least growth retardation, suggesting the existence of partial GH insensitivity.