Pleiotrophin (PTN) also known as heparin-binding brain mitogen (HBBM) or heparin-binding growth factor 8 (HBGF-8) or neurite growth-promoting factor 1 (NEGF1) or heparin affinity regulatory peptide (HARP) or heparin binding growth associated molecule (HB-GAM) is a protein that in humans is encoded by the PTN gene. Pleiotrophin is an 18-kDa growth factor that has a high affinity for heparin. It is structurally related to midkine and retinoic acid induced heparin-binding protein.