Genotyping IGFBP3 Gene Polymorphism Improves the Diagnostic Efficiency of IGFBP-3 Measurements in the Differential Diagnosis between Growth Hormone Deficiency and Idiopathic Short Stature

Abstract

Genotyping IGFBP3 Gene Polymorphism Improves the Diagnostic Efficiency (DE) of IGFBP-3 Measurements in the Differential Diagnosis between Growth Hormone Deficiency (GHD) and Idiopathic Short Stature (ISS) H. Domené, P. Scaglia, A. Martínez, A. Keselman, V. Pipman, V. Bengolea, L. Karabatas, M. Ropelato, M. Ballerini, J. Heinrich, H. Jasper Centro de Investigaciones Endocrinológicas (CEDIE-CONICET), División de Endocrinología, Hospital de Niños Ricardo Gutiérrez, Buenos Aires, Argentina Background: Serum levels of markers of GH action, such as IGF-I, IGFBP-3 and the acid labile subunit (ALS), have been proposed for use in the diagnosis of GHD during infancy. However, as low IGF-I, IGFBP-3 and ALS levels are found in some children with ISS, this reduces the DE of these markers. Objective: The aim of this study was to determine the DE for GHD of IGF-I, IGFBP-3 and ALS levels before and after taking into consideration the effect of genetic polymorphic variants in the genes encoding these proteins. Subjects and Methods: We enrolled 187 normal (age range, 4.9-16.6 years), 86 ISS (3.1-17.6 years) and 24 GHD (3.1-17.6 years) children. Serum IGF-I and ALS were determined by radioimmunoassays and IGFBP-3 by IRMA and expressed as standard deviation score (SDS) in relation to normal controls. The following polymorphisms were determined: IGF1.PCR1 and rs6220 (C/T) in the IGF1 gene, rs2854744 (-202 A/C) and rs13241830 (-185 C/T) in the IGFBP3 gene and rs3751893 (C/T, D70D) and five single nucleotide polymorphisms in the promoter region, all in the IGFALS gene. Cutoff levels for maximal DE were calculated by ROC analysis. Results: The only statistically significant association between serum level and polymorphism was found for IGFBP-3 and the -202 A/C polymorphism. Values (mean±SEM) in normal subjects were AA: 0.34±0.16, AC: 0.13±0.11, CC: −0.30±0.11; ANOVA: p = 0.0032; AA>CC and AC>CC, p <0.05; linear trend (LT): p = 0.0036. In ISS children, values were AA: −0.14±0.28, AC: -0.81±0.17, CC: −1.25±0.22; ANOVA: p = 0.0147; AA>CC, p <0.05, LT: p = 0.0039. In GHD children there was a nonsignificant trend with AA: −1.87±0.36, AC: −2.47±0.52, CC: −2.87±0.55. Table. Diagnostic efficiency of markers of GH action Test Cutoff SDS Sensitivity (%) Specificity (%) DE (%) IGF-I -2.12 66.7 79.1 77.3 ALS -2.74 66.7 91.9 86.4 IGFBP-3 -1.69 70.8 83.7 80.9 Genotypes AA AC CC -1.26 -1.73 -2.56 70.8 89.5 85.4 Conclusions: ALS levels showed higher specificity and higher overall DE, but also relatively poor sensitivity. Genotype-specific IGFBP-3 cutoff levels improved specificity and DE of IGFBP-3 measurements, reaching a similar DE as ALS measurements but with a slightly higher sensitivity. Moreover, this study extends the association of IGFBP-3 levels with the −202 IGFBP3 gene polymorphism to ISS children.