MPO and microscopic polyangiitis: While paediatric AAV data are limited, Cabral et al. reported in 231 total cases (48 MPA, 183 GPA) PR3-ANCA and/or c-ANCA positivity in 67% GPA and 17% MPA in young people with AAV, and MPO-ANCA and/or p-ANCA positivity in 55% MPA and 26% GPA cases [11].