Determining the normal range for IGF-I, IGFBP-3, and ALS: new reference data based on current internal standards.

BACKGROUND: The measurement of insulin-like growth factors (IGF-I) and insulin-like growth factor-binding protein (IGFBP-3) often serves as first-line testing in children with growth disorders. The role of acid-labile subunit (ALS) as a screening parameter for homozygous or heterozygous mutations of the ALS gene still has to be determined. METHODS: IGF-I, IGFBP-3, and ALS were measured in 252 samples from children and adolescents. Reference curves were fitted using generalized additive model for location, scale and shape (GAMLSS) models and SD-Scores were calculated. Bootstrap analysis was used to quantify the uncertainty of the estimated percentiles. Bland-Altman plots were used to investigate the discrepancy between our newly estimated standard deviation scores (SDS) and SDS calculated on the basis of previous reference data. RESULTS: We present reference data for enzyme-linked immunosorbent assay (ELISA) measurements based on recommended internal standard for IGF-I, IGFBP-3, and ALS suitable for calculation of SD-scores. The Bland-Altman plot shows a rough agreement between the previous SDS calculation and our new one only for SDS around 1; for SDS at -2, an average difference of 0.83 SD was noticed. CONCLUSION: Our IGF-I reference values for the interval of interest in diagnosing growth hormone deficiency (GHD) (prepubertal age) are solid as proved by bootstrap analysis. The difference in calculated SD scores by using data provided previously highlights the importance of using labor and method specific reference data.

Growth Hormone Therapy: Comparison of Short- and Long-Term Outcomes between Children with Growth Hormone Deficiency and Small for Gestational Age.

INTRODUCTION: Direct comparisons of both short-term and long-term auxological outcomes of growth hormone therapy (GHT) between growth hormone deficiency (GHD) and small for gestational age (SGA) are scarce. METHODS: One hundred three patients with GHD and 53 patients with SGA treated at our tertiary center were investigated. Short-term and long-term outcomes were compared between these groups using multivariable linear regression models with adjustment for age, sex, and height at therapy start, also allowing for sex-specific group comparisons. RESULTS: Mean delta height standard deviation scores (SDS) after 1 year of treatment were significantly higher in GHD (0.90, CI: 0.82-0.99) compared to SGA (0.67, CI: 0.54-0.79) (p = 0.003) with no sex difference. As expected, the mean increase in height SDS at final height (FH) was significantly higher in GHD (2.21, CI: 2.00-2.42) compared to SGA (1.05, CI: 0.75-1.35) (p < 0.001), leading to a target height corrected FH of -0.39 SDS (CI: -0.62 to -0.15) in GHD and -1.22 SDS (CI: -1.57 to -0.87) in SGA (p < 0.001). Girls with GHD had a better long-term outcome, as did boys with SGA when compared to the respective opposite sex. The cut-off of delta height of 0.5 SDS during the first year had a low sensitivity to detect long-term non-responders. We found a relation between short-term and long-term outcomes in GHD but not in SGA (adjusted R2 = 0.66 vs. 0.01). CONCLUSION: In contrast to GHD, we observed practically no relationship between 1st-year and long-term outcomes in SGA patients treated with GH.

Fibroblast growth factor 23 and Klotho are present in the growth plate.

INTRODUCTION: Regulation of phosphate homeostasis is essential for mineralization and enchondral ossification. Fibroblast growth factor 23 (FGF23) and its obligatory co-receptor Klotho (KL) play a key role in this process by influencing both renal phosphate reabsorption and vitamin D metabolism. In disease, excessive action of FGF23 leads to hypophosphatemic rickets, while its deficiency causes tumoral calcinosis. Although osteocytes and osteoblasts are widely seen as the primary source of FGF23 under physiological conditions, the origin of systemic FGF23 remains controversial. In this study, we investigated the expression of FGF23 and KL in porcine growth plate cartilage, adjacent tissues, and parenchymal tissues. MATERIALS AND METHODS: Tissue samples were obtained from 4- to 6-week-old piglets. mRNA expression was quantified by real-time PCR and normalized to 18S rRNA. Immunohistochemical staining was performed for FGF23, KL, collagen type X, and FGF receptor 1. Growth plate chondrocyte subpopulations were acquired by collagenase digestion of growth plate explants and subsequent density gradient centrifugation. RESULTS: We could detect both FGF23 and KL mRNA and protein in growth plate chondrocytes. FGF23 expression was mainly found in hypertrophic and resting chondrocytes. Furthermore, significant expression of both genes was observed in bone, liver, and spleen. CONCLUSION: These data challenge previous expression analyses, in particular theories of bone as the exclusive source of FGF23. Moreover, significant expression of FGF23 and KL within the growth plate and adjacent tissues imply a potential local role of FGF23 in chondrocyte differentiation and tissue mineralization.

Diagnostic Value of Serum Acid-Labile Subunit Alone and in combination with IGF-I and IGFBP-3 in the Diagnosis of Growth Hormone Deficiency.

BACKGROUND: The acid-labile subunit (ALS) is a crucial factor in the tertiary complex. IGF-I and IGFBP-3 are routinely measured during the diagnostic work-up for growth hormone deficiency (GHD). The aim of the study is to evaluate the relevance of serum ALS as an additional biomarker in the diagnosis of GHD. METHODS: Ninety-one children undergoing standard diagnostic work-up for GHD were included in this retrospective study. Inclusion criteria were evidence-based auxological cutoffs, IGF-I and IGFBP-3 <-2 SDS at first presentation, at least 1 growth hormone (GH) stimulation test, and IGF-I, IGFBP-3, and ALS measurements on the same day. Statistical analysis was performed by ROC as well as by odds ratio calculations. RESULTS: Forty-seven of 90 participants presented with peak GH values under the cutoff of 7 ng/mL. AUC from a model containing only IGF-I was 0.76 and 0.68 when using only ALS. A model containing IGF-I, IGFBP-3, and ALS (AUC = 0.77) did not improve the result compared to the combination of IGF-I/IGFBP-3 (0.77) or IGF-I/ALS (0.76). Furthermore, the variation in the outcome (GH peak

Insulin-like growth factor I (IGF-1) Ec/Mechano Growth factor--a splice variant of IGF-1 within the growth plate.

Human insulin-like growth factor 1 Ec (IGF-1Ec), also called mechano growth factor (MGF), is a splice variant of insulin-like growth factor 1 (IGF-1), which has been shown in vitro as well as in vivo to induce growth and hypertrophy in mechanically stimulated or damaged muscle. Growth, hypertrophy and responses to mechanical stimulation are important reactions of cartilaginous tissues, especially those in growth plates. Therefore, we wanted to ascertain if MGF is expressed in growth plate cartilage and if it influences proliferation of chondrocytes, as it does in musculoskeletal tissues. MGF expression was analyzed in growth plate and control tissue samples from piglets aged 3 to 6 weeks. Furthermore, growth plate chondrocyte cell culture was used to evaluate the effects of the MGF peptide on proliferation. We showed that MGF is expressed in considerable amounts in the tissues evaluated. We found the MGF peptide to be primarily located in the cytoplasm, and in some instances, it was also found in the nucleus of the cells. Addition of MGF peptides was not associated with growth plate chondrocyte proliferation.

IGF expression patterns and regulation in growth plate chondrocytes.

IGF-I and IGF-II are key regulators of growth and metabolism. Still, data about their expression and distribution within the growth plate in different animal models remain contradictory. Inferences drawn from rodent animal models can only be applied to human conditions to a limited extent as the rodent's growth plate never fuses. In this study, we compared the expression of IGF-I and IGF-II in native growth plates of prepubertal piglets and under different cell culture conditions. We detected IGF-I mRNA expression and abundantly expressed IGF-II within the growth plate. IGF-I expression increased during monolayer cell culture while IGF-II expression dramatically decreased. Our studies revealed that these expression patterns remained unaffected by growth hormone stimulation in vitro. The abundant expression of IGF-II in porcine growth plate tissue, both on the mRNA and on the protein level, suggests that IGF-II also has a role in growth regulation at the early postnatal stage.