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/m2 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. IGF-1 receptor haploinsufficiency presents in 2/100 short small for gestational age (SGA) children; the main predictors are small birth size, short stature, small head size, relatively high IGF-I levels, and developmental delay.