C3 and dense deposit disease: This provides an explanation for the distinction between the three aHUS-associated C3 mutations described here (R592W, R161W and I1157T) and the only functionally characterized dense deposit disease-associated C3 mutant (C3del923DG) (Martínez-Barricarte et al., 2010); they specifically impact the interactions between C3b and MCP or C3b and FH, respectively (Fig. 7).