A novel growth factor, persephin, which belongs to the GDNF/neurturin family of growth factors, is disclosed. The human, mouse and rat amino acid sequences have been identified. Human, mouse and rat persephin genomic DNA sequences have been cloned and sequenced and the respective cDNA sequences identified. In addition, methods for treating degenerative conditions using persephin, methods for detecting persephin gene alterations and methods for detecting and monitoring patient levels of persephin are provided. Methods for identifying additional members of the persephin-neurturin-GDNF family of growth factors are also provided.