In the largest cohort published to date, Cabral et al. [3] reported that PR3-ANCA and/or C-ANCA are positive in 67% of GPA and in 17% of MPA patients, whereas MPO-ANCA and/or P-ANCA are found in 55% of children with MPA and in 26% of those with GPA. Here, MPO is linked to granulomatosis with polyangiitis.