The present invention relates to the expression and regulating growth factors in chrondrocytes and developing cartilage, particularly granulin-epithelin precursor (GEP). The invention relates to the modulation and manipulation of these growth factors, GEP, and/or the molecules they interact with, for instance COMP, in cartilage disorders, including arthritis. Assays and screening methods for the determination of the expression and activity of GEP, or of GEP-COMP, are provided, including for screening for the presence or extent of cartilage or arthritic disease and for identifying modulators or compounds/agents for treatment or prevention of cartilage or arthritic diseases.
