Table 1. Summary of the genetic or acquired complement abnormalities associated with aHUS.

Genetic or acquired abnormalities		Frequency (%)	Main effect of mutant or acquired antibody
Complement regulatory factors	CFH	20%–30%	Impaired CFH binding to C3b and/or glycosaminoglycans on host cell surface Reduced cofactor activity*
	CFH/CFHR hybrid	-	Impaired CFH binding to C3b and/or glycosaminoglycans on host cell surface Competitive interaction with CFH
	CFI	4%–8%	Impaired CFI secretion Reduced proteolytic activity
	MCP	8%–10%	Reduction in MCP expression Reduced C3b binding and cofactor activity
	anti-CFH antibody	5%–20%	Inhibition of the complement regulatory function of CFH
Complement activation factors	C3	4%–8%	Resistance to CFI-mediated inactivation of C3b Formation of hyperactive C3 convertase
	CFB	< 1%–4%	Resistance of convertase to decay by CFH Formation of hyperactive C3 convertase
Coagulation-related factors	THBD	3%–5%	Reduced cofactor activity Diminished activation of TAFI
	DGKE	8%	Upregulation of prothrombotic factors and platelet activation**
	PLG	-	Reduced fibrinolytic activity**
Other	INF2	-	-**

CFH: complement factor H, CFHR: complement factor H related, CFI: complement factor I, MCP: membrane cofactor protein, C3: complement component C3, CFB: complement factor B, THBD: thrombomodulin, DGKE: diacylglycerol kinase epsilon, PLG: plasminogen, INF2: inverted formin 2, TAFI: thrombin-activatable fibrinolysis inhibitor (plasma procarboxypeptidase B)

^*Some predisposing variants reside in N-terminal region of CFH show impaired cofactor activity for CFI.

^**Pathologic mechanism of aHUS caused by DGKE, PLG, INF2 variants has not been well described.