Homozygous deletion of a chromosomal fragment containing the CFHR3 and CFHR1 genes (∆CFHR3/1) has been reported to be protective against diseases such as IgAN14 and age-related macular degeneration (AMD)15–17, but it is a risk factor for atypical hemolytic-uremic syndrome (aHUS)18,19. The gene discussed is CFHR3; the disease is atypical hemolytic-uremic syndrome.