Recently, PAPP-A has been found to be a protease specific for insulin-like growth factors (IGF) binding protein (IGFBP) -4 as well as for IGFBP-5 in vitro (15,16).
The cleavage of IGFBP-4 is in an IGF-dependent manner, whereas the cleavage of IGFBP-5 in an IGF-independent manner.