Most patients with hereditary AT deficiency are heterozygous. There is reduced synthesis of the AT molecule. A gene deletion or frameshift mutation results in a truncated protein which is unstable. Type 2 - The level of AT produced is normal, but the protein is dysfunctional. Venous thrombosis occurs most frequently in the deep veins of the lower extremities.
Thrombotic events begin in mid-late teenage years.
Cerebral vein thrombosis can occur. Homozygosity is fatal in utero. Arterial thrombotic events are not increased. Acquired AT deficiency A. Causes include acute thrombosis, DIC, liver disease, nephrotic syndrome, oral contraceptive use. The AT level corrects to normal after treatment.