C3 and hemolytic-uremic syndrome: In fact, about 50% of patients with primary HUS have rare germline variants or hybrid genes in alternate pathway complement genes mainly coding for factor H, factor I, membrane cofactor protein (MCP/CD46), C3, factor B [32,50,51,52,53,54], or, less commonly in adults, autoantibodies against complement factor H. Most of these rare germline variants occur in the factor H gene (25% of all mutations) [55].