In one study evaluating anti-MAA antibody concentrations across all isotypes (IgA, IgG, IgM) in RA patients compared to both healthy volunteers and three diseased control groups (osteoarthritis, systemic lupus erythematous, spondyloarthropathy), only the IgA isotype was found to be significantly higher28. The gene discussed is CD40LG; the disease is spondyloarthropathy.