Rheumatoid arthritis (RA)
RA is characterised by chronic and erosive polyarthritis or by abnormal growth of synovial tissue which if not aggressively treated causes substantial joint damage and irreversible disability. Early diagnosis is of utmost importance to start immediate treatment in order to inhibit the damage caused by this progressive disease.
The most commonly used test is for rheumatoid factor (RF), autoantibodies directed against the Fc region of IgG. IgM RF occurs in 60-70% of patients but specificity is low due to the presence of RF in other disease states.
Autoantibodies against citrullinated filaggrin and a synthetic form, cyclic citrullinated peptide (CCP), are used as specific markers due to the fact that they are rare in healthy individuals and not commonly found in other inflammatory disease. These serve as an early diagnostic marker and also offer prognostic value on the type of RA present (erosive or non-erosive).
Peptidylarginine deiminase 4 (PAD4) converts arginine residues on filaggrin to citrulline which play a role in epitope recognition by autoantibodies. Vimentin, a target of anti-Sa antibodies, is also found to be present in RA patients with relatively high specificity.
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