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. In liver disease, there is decreased AT levels, but this is not associated with any increased risk of thrombosis. In AT deficiency secondary to nephrotic syndrome, treatment of the nephrotic syndrome with glucocorticoids will enhance AT levels.