In-vitro Ternary Complex Formation (ivTCF) Enhanced by the Addition of IGFBP-3 (TCF+): A Useful Approach for the Assessment of the Function of Human IGFALS Gene Variants

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: SAT 632-648-Pediatric Growth Case Reports
Basic
Saturday, June 15, 2013: 1:45 PM-3:45 PM
Expo Halls ABC (Moscone Center)

Poster Board SAT-646
Horacio M. Domené*1, Paula A. Scaglia1, Liliana Karabatas1, Ana C. Keselman1, Alicia S. Martínez1, Débora Braslavsky1, Sonia V. Bengolea2, Viviana Pipman3, Ignacio Bergadá1 and Héctor G. Jasper1
1Hospital de Niños R. Gutiérrez, Buenos Aires, Argentina, 2Hospital Fernández, Buenos Aires, Argentina, 3Hospital Tornú, Buenos Aires, Argentina
Background: Acid labile subunit (ALS) is crucial for ternary complex formation and therefore, to sustain circulating IGF-I levels. While complete ALS deficiency (ALS-D) is characterized by mild short stature and severe circulating IGF-I and IGFBP-3 deficiencies, first degree relatives, heterozygous carriers for IGFALS gene mutations (HC-FDR), present height, IGF-I and IGFBP-3 levels in between ALS-D and wild type (WT) relatives, suggestive of a gene-dosage effect. In addition, IGFALS genetic variants have been reported in a subgroup of idiopathic short stature (ISS) children.

Objective: The aim of the present study was to assess functional ability for ivTCF in children affected by different degrees of ALS insufficiency.

Subjects and Methods: Levels of IGF-I and ALS were assessed by RIA, IGFBP-3 by CLIA, ivTCF by size exclusion chromatography (Sephacryl S200) both before (TCF#) and after (TCF+) the addition of rhIGFBP-3 (6 µg/ml) and expressed as: (area under the curve/total area)x100. IGFALS gene was completely sequenced. Patients: 7 ALS-D, 7 HC-FDR, 15 prepuberal ISS and 5 prepuberal (PP) and 5 puberal (P) normal controls. ISS children were divided in 3 groups according to IGFALS genotype (HC for allelic variants of IGFALS gene or WT) and levels of IGF-I (normal or low, <-2.0 SDS): G1, HC with low IGF-I; G2, HC with normal IGF-I, and G3, WT with low IGF-I.

Results: One-way ANOVA (p<0.0001) showed lower TCF# in ALS-D (0.65±0.30%; mean±SD) compared to HC-FDR (6.42±3.54), G3 (4.99±2.87), PP (5.72±1.36) and P (9.99±1.80) (p<0.01). Besides G1 (3.15±1.71), G2 (3.61±0.86), G3 and PP were lower than P (p<0.05). TCF+ one-way ANOVA (p<0.0001) was low in ALS-D (2.29±1.14, p<0.001 vs. all others); G1 ISS (26.8±7.1) was significantly lower than G2 (48.4±4.6; p<0.001), G3 (45.9±11.9; p<0.01), and PP controls (43.5±2.6; p<0.05). There were no significant differences among G2, G3 and normal controls. TCF+ in G1 ISS was not different from HC-FDR (39.1±9.3).

Conclusions: Both TCF# and TCF+ allowed distinguishing complete ALS deficient patients from the rest. TCF# was higher in P vs. PP, but in TCF+ this difference disappeared. TCF+ in G1 ISS was significantly reduced when compared to the other ISS groups. These findings suggest that the limited ability shown by TCF+, a more ALS dependent parameter, in some IGFALS variants could contribute to the impairment of the IGF system observed in these subjects, leading to low IGF-I levels associated with some degree of growth deficit.

Nothing to Disclose: HMD, PAS, LK, ACK, ASM, DB, SVB, VP, IB, HGJ

*Please take note of The Endocrine Society's News Embargo Policy at http://www.endo-society.org/endo2013/media.cfm

Sources of Research Support: Supported by Foncyt/Secyt PICT 2010 N°1916.