Data from single-cell sequencing indicated that MMP3 generated from synovial immune cells in anti-citrullinated protein antibodies (ACPA) negative RA patients was significantly upregulated in comparison to that of ACPA positive RA patients (Wu et al., 2021), implying that MMP3 possesses a noteworthy value as a diagnostic and monitoring marker for ACPA negative RA patients (Liang et al., 2022). The gene discussed is PRTN3; the disease is rheumatoid arthritis.