Leiden mutation (G1691A) in the F5 gene

Thrombophilia is a tendency to increased blood clotting, which is influenced by both congenital predisposition and external influences (e.g. exercise regimen, weight, age, smoking, trauma, medication). People with higher blood coagulability are at greater risk of blood clots (thrombi), which can lead to partial or complete closure of blood vessels – most often in deep veins of the lower limbs (deep vein thrombosis). Some of the clot can break free, travel through the venous system and close one of the pulmonary vessels after passing through the heart, i.e. development of a pulmonary embolism. Placental thrombosis can compromise the course of pregnancy. External stimuli for the formation of blood clots include hormonal contraception, hormonal treatment of infertility or pregnancy. 

The FV gene encodes coagulation factor V. This protein plays an important role in the formation of a blood clot in response to damage to the blood vessel wall. Blood clotting is controlled by several proteins. One is activated protein C (APC), which binds to coagulation factor V and generally reduces the preparedness for blood clotting. Factor V deficiency associated with the F5 G1691A gene mutation (Leiden mutation – FVL) reduces the effectiveness of its binding to APC, as manifested by a tendency to increased blood clotting (thrombophilia). It is tested by real-time PCR. This method enables monitoring of the progress of the amplification reaction at any point. Each individual cycle has the same properties as classical PCR, i.e. denaturation of double-stranded DNA, primer mounting, chain extension by Taq DNA polymerase. When annealing, not only the appropriate primers are used, but also probes (specific DNA oligonucleotide sequences) with fluorophores. Detection selectivity is ensured by specific probes.

Before initiating combined oral hormonal contraception and/or hormone replacement therapy (HRT) in women with a positive personal history of TEN or a positive family history of TEN in first-degree relatives (mother, father, siblings and children), in women with primary sterility or recurrent abortions in the first trimester of pregnancy or in any foetal loss after this period of gestation, in pregnant women with a positive personal or family history of TEN (see Section 1) or in severe forms of preeclampsia, foetal retardation, placental abruption and stillbirth, in persons with a history of idiopathic TEN to determine the causative cause and to decide on the duration of anticoagulant therapy. If thrombophilic mutations are positively detected, it is advisable to perform these tests in first-degree relatives. In children older than 12 years, unless there are other reasons to perform this testing sooner, or from another indication after examination in the Thrombotic Centre, or indications are part of the Recommended Practice of the Society for Medical Genetics and Genomics, J. E. Purkyne Czech Medical Society – see https://slg.cz/doporuceni/trombofilni-stavy/