Insulin-like growth factor binding protein-3 generation: An index of growth hormone insensitivity

GH insensitivity may be an inherited condition or may arise as a consequence of disease or malnutrition. Laron syndrome is the most severe form of GH insensitivity, arising from an absent or defective GH receptor. Less severe forms of GH insensitivity, however, may exist, resulting in short stature but in few other features of Laron syndrome. We have identified a heterogeneous group of children with short stature and either high basal (>10 mU/L) or high peak GH levels (>40 mU/L) on GH provocation testing, to examine biochemical markers of GH sensitivity. These children received 4 d of GH (0.1 U/kg) and the increment in IGF-I, IGF binding protein (BP)-3, and GHBP was determined. Eight GHD children, commencing GH therapy, were recruited as positive controls. The two groups could not be differentiated by age, height SDS (SD score), height velocity SDS, or body mass index. IGF-I and IGFBP-3 generation were correlated in all children (ΔSDS IGF-I versus ΔSDS IGFBP- 3, r = 0.49, p = 0.03). Neither basal GHBP levels or the increment in GHBP were predictive of the IGF-I or IGFBP-3 response to GH. The GHI group had a significantly reduced IGFBP-3 response to stimulation with 4 d of GH (median percent increment in IGFBP-3, 26%, versus 72% in the GHD group, p = 0.03); their IGF-I response to GH was also reduced (median % increment in IGF-I 75% versus 144% in the GH deficient group), but this did not achieve significance, p = 0.06. In all children, the percentage rise or ΔSDS in both IGF-I and IGFBP-3 inversely correlated with the GH peak obtained on provocation testing, the latter being the most significant determinant of GH peak. We propose that the 'IGF generation test,' in particular IGFBP-3 generation, can be used in the investigation of partial GH insensitivity. Further work, however, is required to establish diagnostic criteria for partial GH insensitivity.