Factor H and MCP are regulatory proteins of the alternative pathway. 8 Since the description of a genetic association of the disease with the cluster of complement related genes on chromosome 1, several mutations have been reported on the exons coding for the C-terminal domains of FH, which are important for C3b binding. 5, 9- 12 Recently, two groups presented evidence that CD46 mutations may also predispose to HUS. 7, 13 Considering the major role of FH in complement alternative pathway regulation, we speculated that other complement regulators might be involved in the disease process. Briefly, Nunc MaxiSorp ELISA plates (Nunc, Roskilde, Denmark) were coated with goat polyclonal IgG anti-human factor I (Calbiochem, Meudon, France).\n FH deficiencies have been reported in both homozygous and heterozygous forms. 15 Genetic studies have also found several different heterozygous missense mutations between SCR16 and SCR20 suggesting a particular role of the C-terminal domains of the protein relevant to the pathophysiology of HUS. 9, 10, 26, 27 Neumann et al found FH mutations in 13% of 111 patients with atypical HUS. 12 The RCA genomic region contains several candidate genes for HUS including the five human regulators of complement activation proteins: FH, complement receptor type 1 (CR1, CD35), membrane cofactor protein (MCP, CD46), decay accelerating factor (DAF), and C4b-binding protein. 28 Recently, MCP mutations were detected by Richards et al in affected individuals of three families and by Noris et al in one family with low C3 levels. 7, 13 On the other hand, we can speculate that a link between the candidate proteins may be ascribed to the alternative pathway regulation.