Depending on the presence or absence of RF and ACPA in RA patients’ serum, two forms of the disease have been established: Seropositive RA, which represents the most common form and is characterised by the presence of RF and or ACPA antibodies, while seronegative RA is determined by the absence of both RF and ACPA.6 Here, PRTN3 is linked to rheumatoid arthritis.