TRIM21 and synovial sarcoma: The importance of TRIM proteins in regulating immune homeostasis is highlighted by inherited disorders that are associated with some of these genes: TRIM20 (pyrin) is mutated in the inflammatory disease familial Mediterranean fever (FMF) [22], [23] and TRIM21 (Ro52) is one of the autoantigens detected in Sjögren's syndrome (SS) and systemic lupus erythematosus (SLE), two severe autoimmune disorders [24], [25].