<h4>Background</h4>A loss-of-functional mutation (W1183R) in human complement factor H (CFH) is associated with complement-associated hemolytic uremic syndrome; mice carrying a similar mutation (W1206R) in CFH also develop thrombotic microangiopathy but its plasma von Willebrand factor (VWF) multimer sizes were dramatically reduced. The gene discussed is CFH; the disease is thrombotic microangiopathy.