TABLE 3.

Genetic changes in convertase-directed regulators and complement effector molecules that are associations with aHUS^a,^b,^c

Gene	Chromosomal Locus	Frequency in aHUS	Commonly observed genetic changesd	Main effect
Factor H	1q31.3	30%	Mutations	Impaired cell-surface regulation
		3–5%	CFH/CFHR1 hybrid allele
FHR3, FHR1	1q31.3	5–15%	Deletions involving CFHR3 and CFHR1	Impaired cell-surface regulation due to occurrence of anti-FH autoantibodies
FHR1, FHR4	1q31.3		Deletions involving CFHR1 and CFHR4
MCP (CD46)	1q32.2	12%	Mutations	Reduced expression
Factor I	4q25	5–10%	Mutations	Low enzymatic activity
Factor B	6p21.33	1–4%	Mutations	Abnormally stabilized C3 convertase
C3	19p13.3	5%	Mutations	Abnormally stabilized C3 convertase/resistance to inactivation by Factor I

^aFor about half of aHUS cases no predisposing genetic change is detectable.

^bSequence abnormalities in thrombomodulin and DGKE also predispose to aHUS and account for about 5% of cases, but are not listed because they are not convertase-directed regulators.

^cTable is adapted from REF 85.

^dMajority of mutations are heterozygous.