IGF-I Generation Test Research Articles

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.

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.

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.

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.

The insulin-like growth factor I generation test in the investigation of short stature.

Genotypic and phenotypic heterogeneity in patients with growth hormone (GH) insensitivity syndrome suggests that partial defects exist in the GH receptor. The insulin-like growth factor I (IGF-I) generation test was assessed as a means of identifying partial GH receptor defects in a heterogeneous group of 22 prepubertal children with short stature. In a subgroup of nine patients with peak GH levels of 63.7 +/- 3.7 mU/l during a glucagon tolerance test, the response to the IGF-I generation test was no different from that for the group as a whole (peak GH, 43.3 +/- 4.5 mU/l), despite the fact that this subgroup exhibited a negative relationship between height SDS and peak GH and a positive relationship between height SDS and IGF binding protein-3. This preliminary study therefore suggests that the IGF-I generation test in its present form will not be useful as a primary screening test for partial GH insensitivity. Despite this, the IGF-I generation test has been extremely useful in the confirmation of the diagnosis of GHIS and may therefore also prove useful in the confirmation of partial defects in the GH receptor. A subgroup of short children with peak GH levels above 40 mU/l had some characteristics of partial GH receptor deficiency. These children, to whom GH therapy would not normally be given, may respond better to recombinant human IGF-I.

Growth Hormone Insensitivity Syndrome (GHIS): Clinical Presentation and Effects of Treatment with Recombinant Human Insulin-like Growth Factor I (rhIGF-I) European Experience

Growth hormone insensitivity syndrome (GHIS) is a pathological state characterised by disturbance of the normal relationships between growth hormone (GH) secretion, insulin-like growth factor I (IGF-I) synthesis and GH action. Laron syndrome (LS) is the most severe form and is related to defects of the GH receptor gene. Twenty-seven cases of IS from 8 European countries and Australia were characterised clinically and endocrinologically. Clinical features (median) were; age 2.8-22.6 years, 12 males, 15 females, birth weight -0.72 SDS, birth length -1.59 SDS. Hypoglycaemia occurred in 33% and micropenis in 58% of males. Height was -6.0 SDS, weight -3.2 SDS, % weight for height 111.3. Bone age was delayed in 19 of the 27 patients. Endocrine values (median) were; GH 17μg/L, IGF-I<5th centile, with% increment during IGF-I generation test <20%. IG1411313-3 was <5th centile, GH-BP was low or undetectable in 20 and normal in 7 subjects.Treatment with recombinant IGF-I offered the only form of effective therapy. Treatment of 13 patients with IGF-I, 120μg/kg bid induced a change in mean height velocity from 4.1cm/year before treatment to 10.2cm/year at 6 months and 8.8cm/year at 12 months. Adverse effects were minimal. Facial appearance showed a change in maturity associated with capital hair growth. Further studies to define the optimum dose regimen of IGF-I are in progress.

Clinical features and endocrine status in patients with growth hormone insensitivity (Laron syndrome).

Twenty-seven patients with GH insensitivity were identified from 44 possible cases, using a scoring system based on height standard deviation score (SDS), basal GH, insulin-like growth factor-I (IGF-I), IGF-I response to IGF-I generation test, and GH-binding protein (GH-BP) determinations. The 27 cases were from 8 European countries and Australia. Clinical features were as follows: age 2.8-22.6 yr; 12 male, 15 female, 19 prepubertal. Birth weight was median -0.72 SDS (1.75(-)-3.29) and birth length, median -1.59 SDS (0.63(-)-3.63). Hypoglycemia had been documented in 33% of the cases, and micropenis was present in 58% of the males. At assessment, height was median -6.1 SDS (-3.8(-)-10.2), weight was median -3.2 SDS (-0.1 to -5.2), and percentage weight for height, median 111.3 (72-271). Puberty was absent in 2 boys aged 15 yr and in 3 girls aged 13 yr. Bone age was delayed in 19 of the 27 patients. Endocrine investigations showed basal serum GH median 17 micrograms/L (0.5-79), IGF-I values less than 5th percentile, and all except 2, age less than 8 yr, less than 0.1 percentile for age. Percentage increment of IGF-I during IGF-I generation test (hGH 0.1 U/kg body weight daily x 4) did not exceed twice the intraassay coefficient of variation, being less than 0.1 percentile for age. IGF-II was median 135.0 micrograms/L (62-232), all values being less than 5th percentile for age. Insulin-like growth factor binding protein-3 (IGFBP-3) values were median 0.53 mg/L (0.10-1.17 mg/L), all being less than 5th percentile for age. IGFBP-3 values after hGH remained less than 5th percentile. IGFBP-1 values showed the normal fall with age, some being above the normal range; IGFBP-2 values were normal. There was a positive correlation between height SDS and IGF-II SDS (r = 0.66, P < 0.001) and IGFBP-3 (r = 0.64, P < 0.001). Specific binding of [125I]hGH to GH-BP was undetectable in 18 patients and extremely low (< or = 5.6%) in 2. GH-BP was normal (14.2-45.9% radioactivity) in 7 subjects, all female, demonstrating that normal GH-BP does not exclude GH insensitivity.

Prospective clinical trial of human growth hormone in short children without growth hormone deficiency

Ten unselected, apparently healthy short children who were capable of normal growth hormone secretion were given human growth hormone (0.1 U/kg 1M thrice weekly) for 6 months to determine whether such treatment might lead to an increase in growth velocity. During treatment, all patients increased their growth rate (from 4.3 +/- 0.3 cm/yr to 7.4 +/- 0.5 cm/yr P less than 0.001). No adverse effects were detected. During the four-day IGF generation test, IGF I and IGF II levels rose significantly from 0.32 +/- 0.04 U/ml to 0.62 +/- 0.13 U/ml and from 279 +/- 36 ng/ml to 434 +/- 49 ng/ml, respectively. However, the growth response was not predicted by either the acute rise in IGF I or that in IGF II. Human growth hormone in standard doses may be capable of inducing accelerated growth in some short children without growth hormone deficiency. Measurements of IGF I and II cannot be used to predict which children will respond.