Table 1.

A pathophysiolgy- and etiology-based classification of thrombotic microangiopathy

Clinical entity	Affected molecule	Cause	Etiology
TTP	ADAMTS13	ADAMTS13 inhibitory antibody	Ticlopidine, HIV, or idiopathic (most cases)
		ADAMTS13 mutations	Hereditary (autosomal recessive)
Atypical HUS	CFH	CFH mutation	Hereditary (autosomal dominant, variable penetrance)
		CFH antibody	Acquired
	MCP	MCP mutation	Hereditary (autosomal dominant, variable penetrance)
	IF	IF mutation	Hereditary (autosomal dominant, variable penetrance)
	BF	BF mutation (gain of function)	Hereditary (autosomal dominant)
	Unknown	Unknown	Unknown (50%–70% of atypical HUS)
Secondary HUS
Stx-HUS	Shiga toxins	Bacterial infection	Stx+ E. coli or Sh. dysenteriae
TF-HUS	TF antigen	Bacterial infection	Bacterial neuraminidase (S. pneumoniae and other organisms)
Others	Unknown	Unknown	Lupus and related disorders, bone marrow/stem cell transplantation, neoplastic diseases, drugs, surgery, pregnancy (HELLP), pancreatitis, etc.
Other TMA*
PNH	CSRF	PIG-A	Somatic mutation
Tumor cell embolism	Unknown	Embolism of tumor cells	Metastasizing malignancies
Others	Unknown	Unknown	Unknown

^*Not association with severe ADAMTS13 deficiency or renal abnormalities

Abbreviations. BF: complement B factor; CFH: complement factor H; CRSF: complement regulating surface proteins (e.g. CD55, CD59); IF: complement factor I; MCP: membrane cofactor protein; PNH: paroxysmal nocturnal hemoglobinuria; Stx: shiga toxins; TF: Thomsen–Friedenreich antigen; TMA: thrombotic microangiopathy