OR20-2 FOUR NOVEL IGF1R GENE HETEROZYGOUS MUTATIONS IN UNRELATED CHILDREN WITH PRE AND POSTNATAL GROWTH RETARDATION AND MICROCEPHALY

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: OR20-Genetics of Growth
Bench to Bedside
Sunday, June 16, 2013: 11:15 AM-12:45 PM
Presentation Start Time: 11:30 AM
Room 122 (Moscone Center)
Matias Juanes*, Roxana Marino, Esperanza Beatriz Berensztein, Gabriela Guercio, Diana Monica Warman, Marta Ciaccio, Silvia Gil, Marco A Rivarola and Alicia Belgorosky
Hospital de Pediatria Garrahan, Buenos Aires, Argentina
IGF-I is essential for normal human growth and mediates its effects through the IGF1R. IGF1R gene mutations have been associated with varying degrees of intrauterine and postnatal growth retardation. The aims of this study were to identify and characterize IGF1R gene mutations in a cohort of 22 patients with pre and postnatal growth retardation and microcephaly, compatible with IGF-1 insensitivity. Direct DNA sequencing was used to identify IGF1R gene mutations. In silico tools were used to predict the pathogenicity of the variations. Functional analysis was performed by evaluating IGF-1 stimulate DNA synthesis in fibroblast cell primary cultures. Results: four novel heterozygous missense mutations in IGF1R gene were detected in four unrelated patients, de novo p.Arg1256Ser (P1), de novo p.Asn359Tyr (P2), p.Arg1337Cys (P3) and p.Tyr865Cys (P4) in the Tyrosine Kinases, ligand binding L2, C-tail and Fibronectin type III-3 domains of the mature protein, respectively.The aminoacid substitutions were located at highly conserved aminoacid residues in the protein.These mutations were predicted to affect protein function using the sequence homology based SIFT tool, the structure-based PolyPhen approach and the Mutation Taster. P3´s father and sister and P4´s mother carrying the p.Arg1337C and p.Tyr865Cys mutation respectively had asymptomatic clinical phenotype. To elucidate the function of the mutated IGF1R we measured IGF-1 dependent DNA synthesis in fibroblast cell primary cultures from P1, P2, P3, P4 and two control subject (C1 and C2) by 3[H]thymidine incorporation into DNA treated with IGF-1(50ng/ml) for 16, 20 and 24 hs. We observed that IGF-1 significantly induced DNA synthesis in C1 and C2 at 20hs (5.15 ± 0.67 and 6.37 ± 1.00 fold increase over basal respectively; p<0.05 by ANOVA and Student Newman Keuls Test). However, no significant increase was observed in any of the four patients studied. Conclusion:We report and characterize four novel heterozygous mutations in the IGF1Rgene, de novo p.Arg1256Ser, de novo p.Asn359Tyr, p.Arg1337Cys and p.Tyr865Cys. These mutations lead to inhibition of cell proliferation induced by IGF-1. These findings strongly suggest that these mutations lead to a failure in the IGF1R activation pathway which would explain the pre and postnatal growth retardation. IGF1R molecular studies should be considered in children with an undiagnosed history of SGA without postnatal catch-up growth and microcephaly. However, the clinical and biochemical pictures among subjects carrying IGF1R haploinsufficiencies are quite variable suggesting that other modulate IGF1 resistance.

 

Nothing to Disclose: MJ, RM, EBB, GG, DMW, MC, SG, MAR, AB

*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 PICT-2008-0347. Argentina