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. Highly expressed in adult liver, but also in kidney, lung, brain, spleen, testis and ovary. Expressed embryos at day 11.5. Also expressed in fetal livers with expression increasing dramatically after birth. Expression decreases only slightly after postnatal day 3 and remains abundant thereafter. The C-terminus is required for IGF-binding and growth inhibition. O-glycosylated.