PROS1 and deep vein thrombosis: In the group of patients that were tested for the presence of a genetic abnormality predisposing to thrombosis, 28/167 (16.8%) had a genetic mutation: nine were heterozygous for factor V Leiden, 10 had prothrombin G20210A mutation, three had homozygous MTHFR mutation with hyperhomocysteinemia, two had factor V Leiden heterozygosity and hyperhomocysteinemia, three had a deficit of protein S and one had prothrombin G20210A mutation and protein C deficiency.