PRTN3 and systemic sclerosis: Within the ANCA + SSc patient cohort, those that are anti-MPO + had a higherfrequency of ATA positivity compared to those that were not anti-MPO + .22 However, the frequency of ANCA, anti-MPO or anti-PR3 in SSc is likelyto be lower than reported, as ANCA testing is not routine in asymptomaticpatients