Genetic Tests
What Is the Prothrombin G20210A Mutation?
The Prothrombin G20210A mutation raises clotting Factor II levels — the second most common inherited thrombophilia. Carrier status, risks and pregnancy implications.
7 min · 22 July 2025
Prothrombin (Factor II) is a central clotting factor — the thrombin precursor. The G20210A mutation in the 3' region of the Factor II gene increases gene expression, raising blood prothrombin levels; higher prothrombin increases clotting tendency.
Prevalence and Inheritance
Heterozygous carriage occurs in roughly 2-3% of European-origin populations, similar in Türkiye; very rare in Asian and African populations. It is inherited autosomal dominant: a carrier parent passes it to each child with 50% probability.
Thrombosis Risk
- Heterozygous: Lifetime thrombosis risk rises about 2.5-3.5 fold; low absolute annual risk. Slightly less risky than FVL.
- Homozygous: Very rare; risk is considerably higher.
- Combined with FVL: Risk multiplies; aggressive prevention and family screening needed.
- Pregnancy: The Prothrombin mutation is among the variants with strong associations to pregnancy thrombosis and loss; carriers planning pregnancy should definitely receive counseling.
Symptoms and Triggers
Carrier status itself is asymptomatic. Risk rises sharply with estrogen-containing drugs, pregnancy/puerperium, surgery, prolonged immobility and obesity. Symptoms are those of DVT and pulmonary embolism (leg swelling-pain; sudden dyspnea).
How Is It Tested?
After DNA isolation from a blood sample, the G20210A region is analyzed by PCR. Results are reported as normal (G/G), heterozygous (G/A) or homozygous (A/A). The test is unaffected by medications or event timing and can be done anytime. If found in a family, first-degree relative screening is recommended.
Roadmap for Carriers
- Avoid estrogen-containing contraception.
- Discuss prophylaxis with your physician for surgery, long journeys and bed rest.
- Healthy weight, regular movement, smoking cessation.
- Preconception counseling when planning pregnancy; prophylaxis during pregnancy if high risk is identified.
- Prompt evaluation if symptoms develop: early diagnosis simplifies treatment.
Conclusion
Prothrombin G20210A is a common, manageable genetic risk marker. Carrier status is not a disease; correctly interpreted, the result safely shapes decisions from family planning to surgical preparation.