NRTN and central nervous system cancer: GDNF is a neurotrophic factor purified for the first time from a rat glioma cell line (B49) [147] and belongs together with neurturin (NRTN), artemin (ARTN), and persephin (PSPN) to the family of GDNF ligands (GFL) belonging in turn to the superfamily of transforming growth factor β (TGF-β) [148].