Our previous studies demonstrated that in Bagg Albino (BALB/c) mice, human aggrecan (partially depleted in its GAG chains) can provoke a chronic, progressive autoimmune polyarthritis (proteoglycan aggrecan-induced arthritis [PGIA]) that is similar to human RA, and the disease can be transferred to naïve syngeneic mice [9]. The gene discussed is ACAN; the disease is arthritic joint disease.