In 1994, researchers in Leiden identified Factor V Leiden, a common inherited variant that increases the tendency to form abnormal blood clots. It explained many cases of familial thrombophilia. The discovery improved risk assessment for deep vein thrombosis and pulmonary embolism.

The identification of Factor V Leiden in 1994 modernized the understanding of inherited clotting risks, linking family history with genetic detail. In literature, this discovery reshaped the ancient concept of blood inheritance, infusing it with contemporary relevance and precision.