One such informative approach was recently illustrated by the finding that alternative pathway inhibition of FB by the small molecule iptacopan resulted in the expected decrease in C3 fragment binding to red blood cells (Peffault de Latour et al., 2024) in patients with paroxysmal nocturnal hemoglobinuria (PNH), which was an effect found when patients are treated only with C5 inhibition and C3 activation continues unabated (Risitano, 2012). The gene discussed is C3; the disease is paroxysmal nocturnal hemoglobinuria.