To the Editor: In their review of the causes of Budd–Chiari syndrome (BCS), Garcia-Pagán and Valla (April 6 issue) 1 note that myeloproliferative neoplasms are the most frequent underlying condition leading to BCS and therefore recommend testing for driver somatic mutations of JAK2 , CALR , and MPL . In patients with triple-negative myeloproliferative neoplasms, they suggest performing next-generation sequencing, particularly for the detection of mutations with a low allele burden or noncanonical mutations, to improve diagnostic accuracy. 2 Among 2664 patients with myeloproliferative neoplasms in our single-center cohort, BCS was observed in only 16 (0.6%), all of whom had a JAK2 V617F mutation. Given . . .