TRAF1 and rheumatoid arthritis: In addition to human leucocyte antigen (HLA) [3] – the first identified genetic risk factor – and four other replicated regions – including the protein tyrosine phosphatase N22 gene (PTPN22) [4], the TNF receptor-associated factor 1 gene (TRAF1)/complement component factor 5 (C5) locus [5-7], the 6q23 locus near the TNFα-induced protein 3 gene (TNFAIP3) [8,9], and the signal transducer and activator of transcription 4 (STAT4) gene [10,11] – a new genetic region associated with RA was described in the Dutch population [12].