MTHFR and hyperhomocysteinemia: For this reason, children with EHPVT, and especially those that associate other risk factors (UVC), should be screened for inherited prothrombotic disorders: prothrombin 20210 mutation (PTHR), factor V Leiden (FVL), methylenetetrahydrofolate reductase (MTHFR) genes deficiency, or metabolic defects like hyper-homocysteinemia.