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

Characterization of an activating R1353H insulin-like growth factor 1 receptor variant in a male with extreme tall height

OBJECTIVE

The insulin-like growth factor1 receptor (IGF1R) is important in growth and development, and inactivating IGF1R mutations cause short stature and relatively high levels of serum IGF-I. We identified an unclassified IGF1R^R1353H variant in a male with extreme tall height, very low levels of serum IGF-I and delayed and prolonged growth spurt. The index case's mother and three sons all carried the variant, but so far only the eldest son (age 18 years) presented with tall height. We hypothesized that the variant could constitute an activating mutation.

DESIGN

The IGF1R^R1353H variant was investigated in Igf1r^-/- mouse embryonic fibroblasts (R-cells) by cell cycle, colony formation and transcriptome analyses.

RESULTS

The IGF1R^R1353H (R-1353) exhibited significantly increased cell proliferation, G1-S progression and colony formation in soft agar. RNA sequencing identified 195 differentially expressed genes between R-WT and R-1353 (adjusted P < 1E-100). Most genes were upregulated in R-1353, including the gene encoding the androgen receptor (AR). Gene expression profiling showed the most significant enrichment in extracellular matrix organization (P = 2.76E-7), collagen biosynthesis (P = 1.21E-5) and cell adhesion (P = 7.38E-5). Retrospective biochemical analysis of the index case revealed decreased testosterone and sex hormone-binding globulin levels, whereas LH and FSH were within normal ranges. This profile suggests an increased sensitivity to androgen, which is compatible with the enhanced expression of Ar in R-1353 cells.

CONCLUSIONS

Our findings suggest that R1353H constitutes an activating IGF1R variant. The possible deregulation of collagen turnover and increased androgen sensitivity implicates an association to tall phenotype in male carriers.

Growth hormone significantly increases the adult height of children with idiopathic short stature: comparison of subgroups and benefit

BACKGROUND

Children with Idiopathic Short Stature do not attain a normal adult height. The improvement of adult height with treatment with recombinant human growth hormone (rhGH), at doses of 0.16 to 0.28 mg/kg/week is modest, usually less that 4 cm, and they remain short as adults. The benefit obtained seems dose dependent and benefits of 7.0 to 8.0 cm have been reported with higher doses of 0.32 to 0.4 mg/kg/week, but the number of studies is limited. The topic has remained controversial.

OBJECTIVE

The objective was to conduct a retrospective analysis of our experience with 123 children with ISS treated with 0.32 ± 0.03 mg/kg/week of rhGH, with the aim of comparing the different subgroups of non-familial short stature, familial short stature, normal puberty, and delayed puberty and to assess the benefit by comparison with 305 untreated historical controls, from nine different randomized and nonrandomized controlled studies.

RESULTS

Eighty eight of our children (68 males and 20 females) attained an adult height or near adult height of -0.71 SDS (0.74 SD) (95% CI, -0.87 to -0.55) with a benefit over untreated controls of 9.5 cm (7.4 to 11.6 cm) for males and 8.6 cm (6.7 to 10.5 cm) for females. In the analysis of the subgroups, the adult height and adult height gain of children with non-familial short stature were significantly higher than of familial short stature. No difference was found in the cohorts with normal or delayed puberty in any of the subgroups, except between the non-familial short stature and familial short stature puberty cohorts. This has implications for the interpretation of the benefit of treatment in studies where the number of children with familial short stature in the controls or treated subjects is not known. The treatment was safe. There were no significant adverse events. The IGF-1 values were essentially within the levels expected for the stages of puberty.

CONCLUSION

Our experience was quite positive with normalization of the heights and growth of the children during childhood and the attainment of normal adult heights, the main two aims of treatment.

Sotos syndrome is associated with deregulation of the MAPK/ERK-signaling pathway

Sotos syndrome (SoS) is characterized by tall stature, characteristic craniofacial features and mental retardation. It is caused by haploinsufficiency of the NSD1 gene. In this study, our objective was to identify downstream effectors of NSD1 and to map these effectors in signaling pathways associated with growth. Genome-wide expression studies were performed on dermal fibroblasts from SoS patients with a confirmed NSD1 abnormality. To substantiate those results, phosphorylation, siRNA and transfection experiments were performed. A significant association was demonstrated with the Mitogen-Activated Protein Kinase (MAPK) pathway. Members of the fibroblast growth factor family such as FGF4 and FGF13 contributed strongly to the differential expression in this pathway. In addition, a diminished activity state of the MAPK/ERK pathway was demonstrated in SoS. The Ras Interacting Protein 1 (RASIP1) was identified to exhibit upregulated expression in SoS. It was shown that RASIP1 dose-dependently potentiated bFGF induced expression of the MAPK responsive SBE reporter providing further support for a link between NSD1 and the MAPK/ERK signaling pathway. Additionally, we demonstrated NSD1 expression in the terminally differentiated hypertrophic chondrocytes of normal human epiphyseal growth plates. In short stature syndromes such as hypochondroplasia and Noonan syndrome, the activation level of the FGF-MAPK/ERK-pathway in epiphyseal growth plates is a determining factor for statural growth. In analogy, we propose that deregulation of the MAPK/ERK pathway in SoS results in altered hypertrophic differentiation of NSD1 expressing chondrocytes and may be a determining factor in statural overgrowth and accelerated skeletal maturation in SoS.

Reduced pericellular sensitivity to IGF-I in fibroblasts from girls with Turner syndrome: a mechanism to impair clinical responses to GH

Girls with Turner syndrome (TS) are treated with supraphysiological doses of growth hormone (GH) to improve final height; however in some girls, the growth response can be poor. This may reflect aberrations in GH and/or IGF-I actions at the cellular level, and thus this study compared the response of skin fibroblasts from normal children (n = 5) and girls with TS (n = 8) to GH, IGF-I, or a combination, by assessing the IGF binding protein (IGFBP) profile of conditioned medium harvested over 7 d. The two cell types had a comparable IGFBP profile; IGFBP-3 and IGFBP-4 were the most abundant species. TS fibroblasts produced more IGFBP-3 (d 7, 51.4 ± 45 ng/mL versus 20 ± 22 ng/mL; p < 0.05) than control cells; levels of IGFBP-4 were similar (21 ± 12 ng/mL versus 30 ± 21 ng/mL). GH did not influence IGFBP production. IGF-I treatment did not affect IGFBP-4 levels but enhanced the production of IGFBP-3 by both cell types (p < 0.05). However, the response of TS fibroblasts to IGF-I was approximately half that observed in normal cells (p < 0.05). Altered IGF-I activity, because of reduced bioavailability and/or reduced sensitivity, could contribute to the need for high GH doses in TS and for the poor response to GH in some girls with TS.

High-dose GH treatment limited to the prepubertal period in young children with idiopathic short stature does not increase adult height

OBJECTIVE

To assess the long-term effect of prepubertal high-dose GH treatment on growth in children with idiopathic short stature (ISS).

DESIGN AND METHODS

Forty children with no signs of puberty, age at start 4-8 years (girls) or 4-10 years (boys), height SDS <-2.0 SDS, and birth length >-2.0 SDS, were randomly allocated to receive GH at a dose of 2 mg/m(2) per day (equivalent to 75 microg/kg per day at start and 64 microg/kg per day at stop) until the onset of puberty for at least 2 years (preceded by two 3-month periods of treatment with low or intermediate doses of GH separated by two washout periods of 3 months) or no treatment. In 28 cases, adult height (AH) was assessed at a mean (S.D.) age of 20.4 (2.3) years.

RESULTS

GH-treated children (mean treatment period on high-dose GH 2.3 years (range 1.2-5.0 years)) showed an increased mean height SDS at discontinuation of the treatment compared with the controls (-1.3 (0.8) SDS versus -2.6 (0.8) SDS respectively). However, bone maturation was significantly accelerated in the GH-treated group compared with the controls (1.6 (0.4) versus 1.0 (0.2) years per year, respectively), and pubertal onset tended to advance. After an untreated interval of 3-12 years, AH was -2.1 (0.7) and -1.9 (0.6) in the GH-treated and control groups respectively. Age was a positive predictor of adult height gain.

CONCLUSION

High-dose GH treatment restricted to the prepubertal period in young ISS children augments height gain during treatment, but accelerates bone maturation, resulting in a similar adult height compared with the untreated controls.

Two short children born small for gestational age with insulin-like growth factor 1 receptor haploinsufficiency illustrate the heterogeneity of its phenotype

CONTEXT

Small for gestational age (SGA)-born children comprise a heterogeneous group in which only few genetic causes have been identified.

OBJECTIVE

To determine copy number variations in 18 growth-related genes in 100 SGA children with persistent short stature.

METHODS

Copy number variations in 18 growth-related genes (SHOX, GH1, GHR, IGF1, IGF1R, IGF2, IGFBP1-6, NSD1, GRB10, STAT5B, ALS, SOCS2, and SOCS3) were determined by an "in house" multiplex ligation-dependent probe amplification kit. The deletions were further characterized by single-nucleotide polymorphism array analysis.

RESULTS

Two heterozygous de novo insulin-like growth factor 1 receptor (IGF1R) deletions were found: a deletion of the complete IGF1R gene (15q26.3, exons 1-21), including distally flanking sequences, and a deletion comprising exons 3-21, extending further into the telomeric region. In one case, serum IGF-I was low (-2.78 sd score), probably because of a coexisting growth hormone (GH) deficiency. Both children increased their height during GH treatment (1 mg/m(2) per day). Functional studies in skin fibroblast cultures demonstrated similar levels of IGF1R autophosphorylation and a reduced activation of protein kinase B/Akt upon a challenge with IGF-I in comparison with controls.

CONCLUSIONS

IGF1R haploinsufficiency was present in 2 of 100 short SGA children. GH therapy resulted in moderate catch-up growth in our patients. A review of the literature shows that small birth size, short stature, small head size, relatively high IGF-I levels, developmental delay, and micrognathia are the main predictors for an IGF1R deletion.

A variable degree of intrauterine and postnatal growth retardation in a family with a missense mutation in the insulin-like growth factor I receptor

CONTEXT

The type 1 IGF-I receptor (IGF1R) mediates the biological functions of IGF-I. Binding of IGF-I to the IGF1R results in autophosphorylation of the intracellular beta-subunit and activation of intracellular signaling.

OBJECTIVE

The objective of this study was to evaluate the functional characteristics of a novel IGF1R mutation and describe the phenotypic features of two patients with this mutation.

DESIGN

The study was performed in a university hospital.

PATIENTS

We describe a 35-yr-old female with mild intrauterine growth failure, progressive postnatal growth retardation, severe failure to thrive, and microcephaly. Her daughter was born with severe intrauterine growth retardation and also showed postnatal failure to thrive and microcephaly.

RESULTS

We found a heterozygous G3148-->A nucleotide substitution in the IGF1R gene, changing a negatively charged glutamic acid at position 1050 into a positively charged lysine residue (E1050K). E1050 is a conserved residue in the intracellular kinase domain. Dermal fibroblasts of the mother showed normal binding of iodinated IGF-I, but autophosphorylation and activation of downstream signaling cascades upon challenging with IGF-I was markedly reduced. Consequently, the maximal [(3)H]thymidine incorporation upon challenge with a dose range of IGF-I was reduced compared with a panel of control cells (3.65 +/- 1.79-fold vs. 6.75 +/- 4.7-fold stimulation; P < 0.01). These data suggest that the mutation results in the inactivation of one copy of the IGF1R gene.

CONCLUSIONS

These two patients support the key role for IGF-I in intrauterine and postnatal growth. The different phenotypes of these and earlier described patients may be associated with variability in IGF-I signaling. The degree of intrauterine growth retardation may be partially determined by the presence or absence of maternal IGF-I resistance.

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

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

Structural and functional characteristics of the Val44Met insulin-like growth factor I missense mutation: correlation with effects on growth and development

We have previously described the phenotype resulting from a missense mutation in the IGF-I gene, which leads to expression of IGF-I with a methionine instead of a valine at position 44 (Val44Met IGF-I). This mutation caused severe growth and mental retardation as well as deafness evident at birth and growth retardation in childhood, but is relatively well tolerated in adulthood. We have conducted a biochemical and structural analysis of Val44Met IGF-I to provide a molecular basis for the phenotype observed. Val44Met IGF-I exhibits a 90-fold decrease in type 1 IGF receptor (IGF-1R) binding compared with wild-type human IGF-I and only poorly stimulates autophosphorylation of the IGF-1R. The ability of Val44Met IGF-I to signal via the extracellular signal-regulated kinase 1/2 and Akt/protein kinase B pathways and to stimulate DNA synthesis is correspondingly poorer. Binding or activation of both insulin receptor isoforms is not detectable even at micromolar concentrations. However, Val44Met IGF-I binds IGF-binding protein-2 (IGFBP-2), IGFBP-3, and IGFBP-6 with equal affinity to IGF-I, suggesting the maintenance of overall structure, particularly in the IGFBP binding domain. Structural analysis by nuclear magnetic resonance confirms retention of near-native structure with only local side-chain disruptions despite the significant loss of function. To our knowledge, our results provide the first structural study of a naturally occurring mutant human IGF-I associated with growth and developmental abnormalities and identifies Val44 as an essential residue involved in the IGF-IGF-1R interaction.