Tests for the causes of thrombophilia (Factor-V Leiden, prothrombin, methylenetetrahydrofolate reductase (MTHFR), plasminogen activator inhibitor-1 (PAI-1), and Factor-XIII mutations) were performed in four patients with two-sided PVT, and the results were reported as normal. Here, MTHFR is linked to Rare hereditary thrombophilia.