Inhibits IGF-mediated growth and developmental rates (By similarity). IGF-binding proteins prolong the half-life of the IGFs and have been shown to either inhibit or stimulate the growth promoting effects of the IGFs on cell culture. They alter the interaction of IGFs with their cell surface receptors. Binds IGF2 more than IGF1. In adults, expressed in brain, testes, ovaries, and kidney. Expression in the adult liver is barely detectable. Predominantly expressed at fetal stages with highest expression in fetal liver. Also expressed in fetal kidney, intestine and lung, as well as muscle, heart and stomach. The C-terminus is required for IGF-binding and growth inhibition. O-glycosylated.