C3 and atypical hemolytic-uremic syndrome: In 40–60% of patients with primary aHUS, genetic abnormalities affecting the complement regulatory proteins factor H (CFH), membrane cofactor protein (MCP), factor I (CFI), and thrombomodulin (THBD) and the components of the alternative pathway C3 convertase C3 and factor B (CFB) or anti-FH autoantibodies have been identified (2, 9–13).