PRTN3 and granulomatosis with polyangiitis: Interestingly these antibodies are frequently detected in sera of MPO- and PR3-ANCA negative patients, and while they can mimic c-ANCA or p-ANCA patterns, they are detected in other types of small vessel vasculitis such as cocaine-induced vasculitis mimicking GPA as well as other autoimmune diseases such as Sjӧgren, rheumatoid arthritis, and ulcerative colitis [9, 15].