Clinically, in peripheral blood mononuclear cells of patients with active MS or with secondary progressive MS, as well as in lymphocytes of patients with rheumatoid arthritis (RA), GRK2 level were shown to be reduced (Lombardi et al., 1999, 2001; Vroon et al., 2003, 2005). Here, GRK2 is linked to rheumatoid arthritis.