Factor V (factor five) is an important intermediary (factor) in blood clot formation. The information to make this protein is available on a gene present in two copies. Normal individuals have two copies of the gene without mutation (“wild” type homozygous). Others have one copy (heterozygous) or two copies (homozygous) of the gene with one modification (mutation) called “R506Q”, “G1691A”, “GA” or “Factor V Leiden”. This mutation is responsible for more than 95% of cases of protein C resistance (another coagulation factor), which increases the risk of clotting (phlebitis, heart attack, stroke, etc.).
Homozygous individuals for the wild type are normal. Heterozygous GA individuals have one copy of the Factor V Leiden and one copy of the wild gene. They may present a thrombosis risk of up to 2 to 3 times the normal risk. Individuals who are homozygous for Factor V Leiden are at high risk for recurrence of thrombosis and may require long-term anticoagulant treatment.