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The dominant antibody at mucous membranes and in exocrine secretions is IgA. It has been implicated in the pathogenesis of rheumatoid arthritis (RA), possibly due to immune complex formation.1,2 If IgA is important in RA pathogenesis one might predict that patients with abnormal levels would have different characteristics from the “normal” IgA population. Limited work published on patients with high IgA levels has suggested that there is an increase in erythrocyte sedimentation rate (ESR), microscopic haematuria, and both distal interphalangeal joint involvement and unilateral sacroiliitis, even though patients fulfil the American College of Rheumatology (ACR) criteria for RA and have no other evidence of spondyloarthropathy.3
Primary selective IgA deficiency is the most common hypogammaglobulinaemia in the general population, with a prevalence of around 1:500.4 It is associated with …