These limitations include the lack of a clear serum or tissue-deposited C3 cut-off correlating with outcome or mortality risk, the normal serum C3 levels in the majority of ANCA-vasculitis patients, the lack of a systemic validation, especially for studies correlating clinical and histological variables, and of course, the lack of association between serum C3 levels and C3 deposition at the sites of tissue damage. This evidence concerns the gene C3 and vasculitis.