Warm autoimmune hemolytic anemia (AIHA) is a rare immune-mediated disorder characterized by IgG-mediated hemolysis and laboratory evidence of anemia, reticulocytosis, elevated lactate dehydrogenase (LDH), indirect hyperbilirubinemia, decreased haptoglobin, and a positive direct antiglobulin test (DAT). The gene discussed is HP; the disease is anemia (phenotype).