Our patient’s high thromboembolic burden and the presence of elevated IgM anticardiolipin antibodies initially raised concerns for antiphospholipid syndrome, although repeat testing was negative, and as a result, the patient does not meet one of the laboratory criteria for diagnosing antiphospholipid syndrome, which is the detection of IgM anticardiolipin antibodies at least 12 weeks apart. The gene discussed is CD40LG; the disease is antiphospholipid syndrome.