Because noncanonical mutations in JAK2 and MPL can be found in a subset of triple-negative myeloproliferative neoplasm (TN-MPN) patients11,12, we sequenced all exons of JAK2 and MPL for all the TN-ET patients (see Methods) and found 4 noncanonical JAK2 or MPL variants in 4 patients: JAK2 I724T (germline), MPL X636WX12 (germline), MPL S204F (somatic), and MPL A58V (unknown status due to a lack of germline control) (Fig. 1B; Table S1). Here, JAK2 is linked to essential thrombocythemia.