Additionally, complement activation has been suggested to play a role in this toxicity, with C5b-9 deposits in muscle biopsies from an MMM case responding to eculizumab (a humanized monoclonal antibody that targets complement C5) (35), and pericapillary C4d deposits in immune-mediated myocarditis cases (36). The gene discussed is C5; the disease is myelofibrosis with myeloid metaplasia.