A recent study developed an isotopic dilution analysis mass spectrometric method to analyze the concentration of citrullinated peptide (CP), anti-CCP, and 4-hydroxyproline (Hyp, a marker of bone turnover and resorption) by biochemical assay to discriminate the type of arthritis at the early stage (within five months of the onset of symptoms of inflammatory arthritis) and advanced arthritis stage in plasma/serum/synovial fluid of patients 87. The gene discussed is CP; the disease is arthritic joint disease.