Pleiotrophin (PTN) is a heparin-binding growth factor with diverse biological activities, the most studied of these being those related to the nervous system, tumor growth and angiogenesis.
MK was induced in human neurofibromas, schwannomas, and various nervous system tumors associated with NF1 or NF2; midkine showed an expression pattern overlapping but distinct from its homolog pleiotrophin (PTN).