Immunoglobulin (Ig)G antibodies (rarely IgM antibodies) generally react with antigens on the RBC surface at body temperature and are thus referred to as “warm agglutinins,” whereas IgM antibodies (rarely IgG type) react with antigens on the RBC surface below body temperature and are thus referred to as “cold agglutinins.” Warm-reacting IgM antibodies may lead to hepatic failure by in vivo autoagglutination [16]. The gene discussed is CD40LG; the disease is liver failure.