Interestingly, a study demonstrating that tacrolimus overcomes P-gp-mediated treatment unresponsiveness in refractory rheumatoid arthritis (RA) patients found that the primary mechanism of P-gp inhibition by tacrolimus is through functionally competitive drug rejection rather than a reduction in P-gp molecules on cells (Suzuki et al., 2010). The gene discussed is PGP; the disease is rheumatoid arthritis.