The complement system, specifically C5, has been implicated in a wide range of pathologies—including Alzheimer's, retinopathies, diabetes, autoimmune disorders, and classical diseases of “complement” such as atypical hemolytic uremic syndrome (aHUS) (Ardissino et al., 2021; Ishii et al., 2021; Krance et al., 2021; Li et al., 2021; Torres et al., 2021; Trakkides et al., 2019). The gene discussed is C5; the disease is diabetes mellitus.