The current, interchangeable use of the epithet “atypical” that may or may not include HUS owing to pneumococcal infection and various metabolic and other conditions, including “secondary” forms of HUS [1, 7] and HUS strictly caused by complement dysregulation (“primary complement-mediated HUS” or “HUS with dysregulation of the APC” [2]), leads to confusion about the etiology of and appropriate therapy for different forms of HUS. This evidence concerns the gene APC and pneumococcal infection.