The JAK2 mutation plays an “all or nothing” pro-thrombotic effect, also with low allelic burden, and can be found in SVT as an isolated positivity; the so-called “solitary JAK2” is more frequently associated with PVT, and up to 52% of the patients could manifest overt MPN during follow-up [22]. This evidence concerns the gene JAK2 and myeloproliferative neoplasm.