Most societies consider homozygosity of factor V Leiden and the prothrombin gene mutation, compound heterozygosity of both, and severe deficiency of factor V Leiden and prothrombin gene mutation as "high risk" thrombophilia and heterozygous for factor V Leiden or the prothrombin gene mutation as "low risk" thrombophilia. This evidence concerns the gene F5 and Rare hereditary thrombophilia.