TRIM21 and synovial sarcoma: Seropositivity against the N-terminal fragment of Ro52 (Ro52-Δ1) in SS was found to highly segregate (Mann Whitney U test p < 0.0001) with RF seropositivity, in which the RF positive SS subjects had a GML of N-terminal Ro52 autoantibodies of 1,572,000 LU (95% CI: 711,100–3,473,000) compared to the RF negative samples of 63,089 LU (95% CI: 27,470–144,900) (Fig. 7A).