Statural development parallels IGF I levels in subjects of constitutionally variant stature

Using a protein-binding assay which measures mainly IGF I, serum levels of insulin-like growth factor (IGF) were determined in 263 children and adolescents of constitutionally variant stature but with normal GH secretion following provocative stimuli. A positive correlation was found between height age and the logarithm of IGF levels (r = 0.67, P less than 0.001). Furthermore, a correlation was found in the tall and short subjects as a group between the ratio of IGF/normal IGF for age and between the ratio of growth rate/normal growth rate for age (r = 0.53, P less than 0.001). Subjects were compared at the same stage of development. At a given bone age or stage of puberty, tall subjects had significantly higher IGF levels than short subjects (P less than 0.005). After the completion of growth, IGF levels in both short and tall subjects stabilized within the normal range. Nevertheless, their mean levels remained significantly different (P less than 0.001). Our results suggest that in normal children and adolescents, differences in IGF I secretion may be at least partially responsible for the individual differences in growth.