The Factor V (FV)
Clinical Features:
The FV Leiden mutation is a significant risk factor for deep vein thrombosis (DVT).
In the United States approximately half a million people per year are
hospitalized due to venous thrombosis. DVT may present as a painful, swollen
area (usually of the leg). If the thrombosis becomes dislodged it may manifest
as a pulmonary embolism with shortness of breath, rapid heartbeat, arrhythmia
or sudden death. Protein C or protein S deficiency or the presence of the FV
Leiden mutation are all risk factors for DVT. The FV Leiden mutation is present
in approximately 20-40% of individuals with symptoms of venous thrombosis,
making it the most frequent risk factor associated with DVT.
Inheritance: Autosomal dominant with variable penetrance.
Individuals with one copy of the mutation (heterozygous positive) have a 50%
chance to pass the gene to each of their offspring.Those with two copies of the
mutation (homozygous positive) have a 100% chance to pass the mutation to each
of their offspring. Risks and risk factors: Heterozygotes with one copy of the
FV Leiden mutation are at a 7-fold increased risk and homozygotes with two
copies of the FV Leiden mutation are at an 80-fold
increased risk for
DVT. Homozygous positive individuals are expected to have at least one
thrombotic event in their lifetime, while heterozygous individuals vary with
respect to the expression of thrombotic problems. Risk factors that may trigger
a thrombotic event include surgery, oral contraceptives, pregnancy, estrogen
replacement therapy and trauma.
Indications and
benefits: Testing is recommended for presymptomatic evaluation of at-risk
individuals and for individuals with a history of DVT. Individuals who are found
to be positive for the FV Leiden mutation can benefit from anticoagulant
therapy and can advise other family members of their risks.
Test methodology: Polymerase chain reaction (PCR)* amplification and
restriction enzyme digestion to detect the presence of the FV Leiden mutation
(506Q) in the gene located at chromosome band 1q21-25. Results are reported as
homozygous negative, heterozygous positive or homozygous positive.
Turnaround: Routine 2-3 weeks, Rush 7-10 days Additional
resources: Factor V testing may have complex genetic issues. We recommend
consultation with a Genetic Counselor in your area, or you may contact us at
the following address