Antithrombin III deficiency (ATIII deficiency) is a deficiency of antithrombin III. Antithrombin is a protein produced by the liver, that inactivates several enzymes of the coagulation system. It causes recurrent thrombosis and pulmonary embolism, and repetitive intrauterine fetal death (IUFD). It is usually autosomal dominant, but can be recessive. It can be caused by kidney failure, especially nephrotic syndrome, which causes antithrombin to be lost in the urine, causing higher factor II and X activity, and increased tendency to clot.