Like idiopathic AIHA, CLL associated AIHA comprises the more frequent warm type, generally due to IgG optimally binding erythrocytes at 37 °C in vitro, and a cold type (cold hemagglutinin disease (CHAD)), usually caused by IgM optimally binding erythrocytes at 4 °C. The gene discussed is CD40LG; the disease is autoimmune hemolytic anemia.