Short answer · Medically reviewed summary · Last updated: 2026-04-07
TL;DR: Antithrombin III deficiency is primarily caused by mutations in the SERPINC1 gene, which leads to a reduced ability of the body to regulate blood clotting. While it is most often inherited in an autosomal dominant pattern, it can also be acquired through secondary conditions such as liver disease, nephrotic syndrome, or disseminated intravascular coagulation (DIC). What causes Antithrombin III deficiency? At its core, Antithrombin III deficiency is a disorder of the coagulation system.
2 people with Antithrombin III deficiency have shared their first-person experience on this question at DiseaseMaps.
Which are the causes of Antithrombin III deficiency?
Causes of Antithrombin III deficiency explained: genetic and environmental factors, reviewed against medical sources, plus patient perspectives.
TL;DR: Antithrombin III deficiency is primarily caused by mutations in the SERPINC1 gene, which leads to a reduced ability of the body to regulate blood clotting. While it is most often inherited in an autosomal dominant pattern, it can also be acquired through secondary conditions such as liver disease, nephrotic syndrome, or disseminated intravascular coagulation (DIC).
What causes Antithrombin III deficiency?
At its core, Antithrombin III deficiency is a disorder of the coagulation system. Under normal circumstances, the protein antithrombin acts as a "natural anticoagulant" or a brake on the blood clotting process, preventing the formation of dangerous clots. In individuals with Antithrombin III deficiency, this brake is either missing, low in quantity, or dysfunctional. This results in a hypercoagulable state, meaning the blood is more prone to clotting than it should be.
How do genetic factors contribute to the condition?
The most common cause of Antithrombin III deficiency is a mutation in the SERPINC1 gene, which provides instructions for producing the antithrombin protein. This condition is inherited in an autosomal dominant pattern, meaning a child has a 50% chance of inheriting the condition if one parent carries the mutation. Geneticists classify these mutations into two main types:
- Type I (Quantitative deficiency): The body produces insufficient amounts of the antithrombin protein.
- Type II (Qualitative deficiency): The body produces enough protein, but the protein itself is structurally abnormal and cannot effectively inhibit clotting factors.
Can Antithrombin III deficiency be acquired?
Not every case of Antithrombin III deficiency is inherited. In some patients, the condition is "acquired" secondary to other systemic illnesses. When the body loses antithrombin faster than it can produce it, or when production is impaired by organ damage, levels drop significantly. Common secondary triggers include:
- Liver Disease: Because the liver is the primary site of antithrombin synthesis, cirrhosis or liver failure can lead to reduced levels.
- Nephrotic Syndrome: This kidney condition causes the body to lose essential proteins through urine, including antithrombin.
- Disseminated Intravascular Coagulation (DIC): During severe illness or trauma, the body "uses up" its clotting inhibitors, causing a temporary but dangerous deficiency.
- Extracorporeal Circulation: Procedures like cardiopulmonary bypass can sometimes lead to a consumption of antithrombin.
Is the etiology fully understood?
While the role of the SERPINC1 gene is well-established, researchers are still working to understand why some individuals with the same genetic mutation experience severe, recurrent blood clots (thrombosis) while others remain asymptomatic throughout their lives. Current research into Antithrombin III deficiency is focused on identifying "modifier genes" and environmental factors—such as smoking, oral contraceptive use, or surgery—that may interact with the genetic deficiency to trigger a clinical event. Within the Antithrombin III deficiency community on DiseaseMaps.org, 42 members have shared their experiences, highlighting the wide spectrum of how this condition presents in real-world scenarios.
What is the difference between a cause and a risk factor?
In medical terms, the cause of Antithrombin III deficiency is the underlying genetic mutation or the physiological process (like liver disease) that lowers antithrombin levels. A risk factor, however, is a circumstance that increases the likelihood that a person with the deficiency will develop a blood clot. For example, pregnancy, long-haul travel, or prolonged immobility are not the causes of the deficiency itself, but they are major risk factors that can turn a latent deficiency into a medical emergency.
Next steps
- Consult a hematologist or a clinical geneticist to discuss genetic testing if you have a family history of unexplained blood clots.
- Keep a record of your medical history, specifically any history of deep vein thrombosis (DVT) or pulmonary embolism (PE), to share with your care team.
- Connect with the 42 members of the DiseaseMaps.org community to share experiences and learn about management strategies.
- Avoid high-risk triggers like smoking or certain hormonal medications unless specifically cleared by your specialist.
Medical disclaimer: This content is for informational purposes only and does not constitute professional medical advice, diagnosis, or treatment; always seek the advice of your physician or other qualified health provider with any questions regarding a medical condition.
References
- NIH Genetic and Rare Diseases Information Center (GARD): Antithrombin deficiency.
- Orphanet: Antithrombin III deficiency.
- OMIM (Online Mendelian Inheritance in Man): SERPINC1 gene entry.
- National Organization for Rare Disorders (NORD): Antithrombin Deficiency page.
Posted May 17, 2017 by Amy 1120
Posted Sep 9, 2017 by Leslie Weinstein 1500
