Pearls on factor V (Leiden) mutation

1. By far the most common genetic risk factor for thrombophilia

2. Mechanism: increases thrombin production

3. Prevalence varies widely by ethnicity: 5.3 percent in whites, 2.2 percent in Hispanics, 1.3 percent in native Americans, 1.2 percent in African Americans, 0.5 percent in Asian Americans.

4. Five to ten percent of heterozygous carriers in their lifetimes; a sevenfold risk over non carriers but homozygous have an 80 fold risk.

5. 90 to 95 percent of patients with protein C resistance have a point mutation of factor V506Q.

6. Other causes of increased protein C resistance include smoking, oral contraceptives, pregnancy, HRT use, cancer, and anti phospholipid syndrome

7. Syndrome is convincingly linked to venous but not arterial thrombotic events

8. Testing in nonwhite populations is low yield

9. Testing in ischemic stroke in absence of a right to left shunt is low yield

10. In presence of a right to left shunt screening for Dvt with leg ultrasound and pelvic venography is useful