While most patients with the hemolytic-uremic syndrome (HUS) have been exposed to Shiga toxin-producing enteric bacteria, some have not. These patients are referred to as having atypical hemolytic uremic syndrome.


Clinical findings:

(1) microangiopathic hemolytic anemia (with schistocytes)

(2) thrombocytopenia

(3) renal failure

(4) other manifestations of thrombotic microangiopathy (headache, seizures, etc)

(5) negative for exposure to Shiga toxin-producing bacteria


Some cases are familial while others are sporadic.


Underlying conditions:

(2) mutations in genes suppressing complement activation (C4b binding protein, factor H, factor I, C3b, membrane cofactor protein, CFH-related proteins, etc)

(1) mutations in genes promoting complement activation (factor B, etc)

(3) mutations in the thrombomodulin gene

(4) other as yet unspecified mutations


The prognosis for atypical HUS is usually poor.


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