50 BODY SIZE AND GROWTH VELOCITY PARALLEL INSULIN-LIKE GROWTH FACTOR (IGF) I LEVELS IN CHILDREN AND ADOLESCENTS WITH CONSTITUTIONAL VARIANT STATURES

Abstract

In subjects with various growth rates (without any clinical or biological abnormalities) IGF I related peptides increase with age in a similar way but at different levels. In comparison with normal subjects (height = mean for age ± 1 SD), IGF levels measured by competitive protein-binding assay were found significantly higher in subjects with tall stature (height > mean for age + 2 SD) and significantly lower in subjects with short stature (height < mean for age - 2 SD). Analysis of the data altogether shows that 1) the positive correlation between IGF and height (r = 0.71, p < 0.001, n = 227) does exist without respect to age, as shown when studying the ratios of height/normal height for age vs IGF/normal IGF for age (r = 0.61, p < 0.001); 2) in subjects whose growth was followed up (tall and short stature) a positive correlation is found between the ratios of growth velocity (gv)/normal gv for age and IGF/normal IGF for age (r = 0.52, p < 0.001, n = 111). The differences in IGF levels between the three groups of subjects (which contrast with no differences in GH levels in the usual pharmacological tests) disappear after epiphyseal fusion. These results suggest that, during growth, individual differences in height and growth velocity seem to be directly related to the IGF secretory capacity. This provides further evidence for an important role of IGF I in the physiological control of growth.