The major known molecular axes of osteoarthritis are the protective TGFβ to SOX9 pathway, which maintains cartilage, and the IL-1β and other inflammatory signals to RUNX2 pathway, which respond to inflammatory and damage signals to prompt repair, expression of degradative enzymes, and development towards bone including hypertrophy and apoptosis of chondrocytes. The gene discussed is SOX9; the disease is osteoarthritis.