Dynamic Changes in Serum IGF-I and Growth During Infancy: Associations to Body Fat, Target Height and PAPPA2 Genotype.

Context Insulin-like growth factor-I (IGF-I) is important for postnatal growth and may be of diagnostic value in infants suspected of pituitary disease. However, little is known about the impact of IGF-I and its determinants on infant growth. Importantly, detailed reference ranges for IGF-I and IGF binding protein-3 (IGFBP-3) concentrations during infancy are lacking. Objective To evaluate the rapid changes in weight and length as well as their determinants in healthy infants, and to establish age- and sex-specific reference curves for IGF-I and IGFBP-3 in children aged 0-1 year. Design Prospective longitudinal study. Setting Cohort study. Participants A total of 233 healthy children (114 girls) with repeated blood samples during first year of life. Main outcome measure(s) Serum concentrations of IGF-I and IGFBP-3, length velocity, weight velocity, and PAPPA2 (rs1325598) genotype. Results Individual trajectories of length and weight velocities were sex specific. We provide detailed reference curves based on longitudinal data for IGF-I and IGFBP-3 during infancy. In both girls and boys, IGF-I decreased during infancy whereas IGFBP-3 remained stable. IGF-I and IGFBP-3, but not PAPPA2 genotype, were positively associated with weight gain, but not with longitudinal growth. When stratified by sex, the association between weight gain and IGF-I only remained significant in girls. Conclusions Interestingly, we found a significant association between IGF-I and infant weight gain in girls, but not with longitudinal growth in the first year of life. Our findings highlight the role of IGF-I as an important anabolic hormone that is not limited to linear growth.