IRF5 and synovial sarcoma: For TRIM21-associated SS, single nucleotide polymorphism (SNP) and genome-wide association (GWAS) studies have identified polymorphisms in HLA, interferon regulatory factor-5 (IRF5) (suggesting TRIM21 is an interferon-stimulated gene; see below), and B cell activating factor (BAFF) loci (12, 13).