Baxter et al identified the association of JAK2 mutation in 59% of patients with Budd–Chiari syndrome (BCS); Smalberg et al [Hematologica 2006 [1]] found a 41% prevalence of this mutation in BCS patients, on a group of 40 patients with primary non–malignant BCS. This evidence concerns the gene JAK2 and hepatic veno-occlusive disease.