Why Some People Develop Blood Clots More Often: The Genetics

Last reviewed: May 12, 2026 Last updated: May 12, 2026

Written by: Jay Hastings , CEO of PlexusDx

Jay Hastings is the CEO of PlexusDx, a precision health company focused on genetic testing, blood biomarker insights, and personalized wellness recommendations. He has more than 20 years of experience across healthcare innovation, genomics, laboratory operations, healthcare investing, and strategic finance. His work has included scaling healthcare startups, leading CLIA lab integrations, and helping expand consumer access to precision health tools.

Medically reviewed by: Jayden Lee, PharmD, EMBA

Jayden Lee, PharmD, EMBA, is the PlexusDx Medical Science Liaison with a PharmD and MBA specializing in pharmacogenomics and clinical product development, with a proven ability to bridge the gap between genomic research and practical patient outcomes. Dr. Lee has more than 10 years of professional experience in clinical pharmacy, academia, and research.

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Some people go through life without a single clotting problem, while others face repeated deep vein thromboses, pulmonary emboli, or clots at a young age. Part of that difference is behavior and circumstance. A meaningful part is written in your DNA. Inherited variation in the proteins that control coagulation can tip the balance toward clotting long before any symptom appears.

Understanding that genetic baseline does not diagnose a clotting disorder, but it does explain why clotting risk is not evenly distributed and why two people in identical situations can have very different outcomes.

How a Blood Clot Actually Forms

Clotting, or coagulation, is a controlled chain reaction. When a vessel is injured, platelets gather and a cascade of clotting factors activates in sequence, converting fibrinogen into fibrin threads that trap cells and seal the wound. Just as important is the braking system: natural anticoagulants such as protein C, protein S, and antithrombin switch the cascade off once the repair is done.

A clot becomes dangerous when this balance fails and coagulation runs ahead of the brakes. When that happens inside an uninjured vein, the result is a thrombosis that can travel to the lungs. Inherited variants that either accelerate the cascade or weaken the brakes are called thrombophilias.

Factor V Leiden and Prothrombin: The Two Most Common Inherited Variants

The single most common inherited thrombophilia in people of European ancestry is Factor V Leiden, caused by the F5 gene variant rs6025. Normally, activated protein C shuts down Factor V to slow clotting. The Leiden variant changes one amino acid so Factor V resists that shut-off signal, a state called activated protein C resistance. Coagulation stays switched on longer than it should.

The second is the prothrombin G20210A variant (the F2 gene, rs1799963), which raises circulating levels of prothrombin, a central clotting factor. Carrying one copy of either variant modestly increases lifetime clot risk; carrying two, or one of each, raises it further. Most carriers never develop a clot, which is exactly why these are predispositions, not verdicts.

MTHFR, Homocysteine, and the Methylation Connection

The MTHFR gene, through common variants such as C677T (rs1801133), influences how efficiently the body processes homocysteine, an amino acid tied to blood-vessel health. Reduced enzyme activity can raise homocysteine levels, and elevated homocysteine has been studied as a contributor to vascular and clotting risk. The relationship is more modest and more context-dependent than the direct thrombophilias, but it sits in the same biological neighborhood and is often part of a fuller genetic picture.

Genetics Rarely Acts Alone

Inherited variants set a baseline, but clots usually appear when that baseline meets a trigger. Prolonged immobility, surgery, pregnancy, estrogen-containing medications, obesity, smoking, and long-haul travel all add coagulation stress. A person with Factor V Leiden may never clot until a triggering event stacks on top of the genetic tendency. This is why the same variant can be silent in one relative and consequential in another.

What Pathway-Level Genetic Insight Adds

The Precision Peptide Genetic Test reads your DNA across 14 pathways, 49 peptides, 150+ genetic insights, mapping the biological pathways that shape processes like coagulation, methylation, and vascular signaling. It is not a diagnosis and it does not tell you whether you will have a clot. It gives you pathway-level context—genetics as a guide, not a guarantee—so a conversation with your provider starts from your actual biology rather than a population average.

Turning Awareness Into a Plan

If you have a personal or family history of clots, clotting at a young age, or recurrent pregnancy loss, share it with a qualified healthcare provider. Clinical thrombophilia testing, when indicated, is ordered and interpreted by that provider, who weighs your genetics alongside your history and current risk factors. Awareness of your genetic tendencies is most useful before a high-risk situation—surgery, a long flight, a new medication—so prevention can be discussed in advance.

Frequently Asked Questions About Genetic Clotting Risk

Does having Factor V Leiden mean I will get a blood clot?

No. Factor V Leiden raises the statistical likelihood of a clot, but most carriers never experience one. The variant is a predisposition, not a diagnosis. Whether a clot forms depends on additional triggers such as surgery, immobility, hormones, or other risk factors layered on top of the inherited tendency.

Which genes are most associated with inherited clotting risk?

The best-established inherited thrombophilias involve the F5 gene (Factor V Leiden, rs6025) and the F2 gene (prothrombin G20210A, rs1799963). MTHFR variants that affect homocysteine metabolism are studied as a more modest contributor. Deficiencies in protein C, protein S, and antithrombin are rarer inherited causes.

Can genetic testing replace a doctor's clotting workup?

No. Genetic insight describes pathway-level tendencies in your biology; it does not diagnose a clotting disorder or measure an active clot. A qualified provider orders clinical thrombophilia testing when your history warrants it and interprets those results alongside your symptoms and overall risk profile.

Curious how your coagulation and methylation pathways are built? Take the Precision Peptide Genetic Test to see how your DNA shapes 14 pathways, 49 peptides, 150+ genetic insights—then bring that context to your provider.

This article is part of the PlexusDx Education Hub. Browse all Blood Testing & Biomarkers education

The Precision Peptide Genetic Test analyzes how your genes influence peptide-related biological pathways. It does not recommend, prescribe, or determine which peptides you should use, and it does not diagnose, treat, cure, or prevent any condition. Consult a qualified healthcare provider before beginning any peptide protocol or making changes to your care.

Medical and Editorial Standards

Medical review process: This article was reviewed for medical accuracy, scientific clarity, evidence alignment, and appropriate discussion of genetics, medications, supplements, biomarkers, and health-related claims.

Sources and evidence: PlexusDx educational content is developed using peer-reviewed research, clinical literature, reputable medical references, and, where applicable, public health or regulatory guidance. References are included at the end of the article when scientific, medical, or health-related claims are discussed.

Commercial transparency: PlexusDx offers genetic testing, blood biomarker testing, personalized supplement recommendations, and related precision wellness services. Product mentions are intended to help readers understand available options and should not be interpreted as medical advice.

Important disclaimer: PlexusDx educational content is for informational purposes only and should not be used as a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making decisions about medications, supplements, genetic testing, lab testing, or health-related care.