Thrombo-embolic venous diseases are represented by deep venous thrombosis and/or pulmonary embolism. In some patients with repeated thrombosis or occurrence of thrombosis in unusual sites, the etiological workup remains negative, which represents a problem for the management of the anticoagulant treatments. Recently, two factors have been identified as important in the physiopathology of hemostasis and coagulation: the presence of clonal hematopoiesis of indetermined potential (CHIP) and the formation of neutrophil extracellular traps (NETs). In this study, these two factors will be studied in patients with repeated venous thrombosis or thrombosis occurring in unusual site.

It has recently been shown that some patients clonal have mutations at a low level in hematopoietic cells (this phenomenon is named clonal hematopoiesis of indetermined potential (CHIP)) and that the presence of a clonal hematopoiesis is associated with an increased cardiovascular risk. However, few data exist about the implication of CHIP in venous thrombosis. Neutrophils extracellular traps are involved in the activation of hemostasis and coagulation. Murine models have highlighted the crucial role of NETs in the physiopathology of venous thrombosis. In patients, studies have demonstrated that NETs markers were present in arteries lesions as coronary plaques. However, few studies have analyzed the NETosis in the setting of venous thrombosis.

The study hypothesis is that patients with venous thrombosis may have an increased prevalence of CHIP and/or an increased NETosis formation, which may represent a predisposition for the occurrence of venous thrombosis. We also speculate that patients with CHIP may have an increased NETosis, due to the presence of activating clonal mutations in neutrophils.

Patients included will be : younger than 50-years-old with repeated thrombosis or thrombosis of unusual sites (cerebral venous thrombosis, splanchnic thrombosis) with a negative etiological workup and notably the absence of constitutional or acquired venous thrombosis risk factors. In this population, we will analyze the prevalence of CHIP and the NETosis via the study of 4 different NETosis plasmatic markers.

Inclusion Criteria:

• Patients (male or female) less than 50 y.o with :
• Splanchnic venous territory thrombosis or
• Cerebral venous thrombosis or
• Venous thrombosis of the upper limb or
• Pulmonary embolism (1st episode if male, 2nd episode if female) unprovoked or
• 1 episode of deep vein thrombosis + 1 episode of arterial thrombosis

Exclusion Criteria:

• Presence of a major or minor transient venous thrombosis risk factor:
• Surgery within the last 3 months preceding the qualifying thrombotic episode
• Lower limb fracture with immobilization > 3 days in the last 3 months preceding the qualifying thrombotic episode
• Presence of estro-progestational contraception
• Pregnancy
• Immobilization for acute medical reasons within the last 3 months preceding the qualifying thrombotic episode
• Air or car travel > 6 hours
• Presence of a major or minor persistent risk factor for venous thrombosis:
• Presence of active cancer (solid cancer or hematologic malignancy)
• Chronic inflammatory digestive or joint diseases
• Ongoing treatment with heparin (low molecular weight heparin (LMWH) or unfractionated heparin (UFH))
• Presence of an abnormality on the thrombophilia test among the following abnormalities
• Protein C deficiency
• Protein S deficiency
• Anti-thrombin deficiency
• Heterozygous or homozygous factor II mutation
• Heterozygous or homozygous factor V mutation
• Presence of anti-phospholipid syndrome
• Presence of myeloproliferative neoplasia
• Presence of paroxysmal nocturnal hemoglobinuria