An endocrinologist's approach to the growth hormone--insulin-like growth factor axis.

Gene knockout studies in mice, and a recent case report, have demonstrated that insulin-like growth factors (IGFs) are major mediators of pre- and postnatal growth, whereas the growth-promoting role of growth hormone (GH) appears to be confined largely to the postnatal period. The IGF axis is now known to consist of the growth factors themselves and at least seven, and probably ten, IGF-binding proteins. These act either by regulating the availability of IGFs to their receptors, or directly on their target cells. Because of the difficulties associated with GH provocative testing, the central role of IGFs in pre- and postnatal growth, and the ease of assaying the various components of the IGF axis, it is suggested that the differential diagnosis of short stature should be based on the concept of IGF deficiency rather than on GH secretory status.