Can inherited blood clotting problems increase my risk of having a stroke?
Blood clotting disorders may be to blame for 5% to 10% of blocked-vessel (ischemic) strokes—possibly more in younger, otherwise healthy people. Typical clotting disorders result in a greater likelihood of clots forming inside of blood vessels, which can cause a blocked-vessel stroke. Clotting disorders that predispose to the formation of blood clots are not risk factors for bleeding (hemorrhagic) stroke. There are some rare inherited disorders that make the blood unable to clot, which does increase the chances of a bleeding stroke.1
What is Factor V Leiden?
The most commonly inherited blood clotting problem is called Factor V Leiden (FVL), so-called because it affects the Factor V (5) clotting protein. FVL occurs in about 5% of white women and men; rates are lower for Hispanics and it is rare in people of Asian or African descent. See Should I be tested for blood clotting problems?
Does FVL increase my risk of stroke?
Inheriting the FVL mutation may increase your risk of stroke in the presence of other risk factors, such as birth control pills. The mutation by itself accounts for an increase in stroke risk less than that associated with the birth control pill alone.2, 3 However, women with a single defective FVL gene have a 30-fold higher risk of developing blood clots while using birth control pills, a 15-fold higher risk with postmenopausal hormone therapy, and a 7-fold higher risk during pregnancy compared with women without this mutation.4, 5 Women who carry two abnormal FVL genes have an even greater risk of developing blood clots. It is likely that these women will experience at least one blood clotting event during their lifetime. Whether the FVL mutation increases stroke risk in younger people without other risk factors is controversial.3, 5 A recent European study of 240 stroke patients found that FVL together with another genetic clotting condition ( prothrombin, discussed below) accounted for an overall 4-fold increased risk of stroke compared with patients with similar risk factors but no genetic clotting condition. Compared with men, women in this study had a greater stroke risk (5-fold) associated with these disorders.6
What other inherited blood clotting problems may be linked to stroke?
A common genetic risk factor for blood clots is a mutation in the gene encoding the clotting factor ‘prothrombin'. The mutation is found in about 1 in 50 persons in the US. It raises the risk of blood clots for both women and men of all ages, but appears to increase stroke risk only if you have other risk factors such as a congenital heart defect (especially Patent Foramen Ovale), other clotting problems, or are taking birth control pills.2, 6-8 If you know you have an inherited blood clotting disorder, or have had a blood clot before, it is very important you address your other risk factors for stroke such as quitting smoking, managing high blood pressure and talking to your doctor about birth control pills.
Results from the Framingham Heart Study showed that one particular blood marker was an independent risk factor for blocked-vessel stroke and transient ischemic attack (TIA) in women but not in men. The blood marker in question is called an anticardiolipin antibody (aCL). aCL is a protein found in the blood that, if present in excessive amounts, is associated with clotting abnormalities as well as multiple pregnancy miscarriages. The study in question found that women with a high level of aCL in their blood were almost 3 times as likely to suffer a blocked-vessel stroke as women with normal aCL levels. No association between stroke and aCL was found for men.9