Essential thrombocythemia (ET) and primary myelofibrosis (PMF) are chronic diseases characterized by clonal hematopoiesis and hyperproliferation of terminally differentiated myeloid cells. The disease is driven by somatic mutations in exon 9 of CALR or exon 10 of MPL or JAK2-V617F in >90% of the cases, whereas the remaining cases are termed "triple negative." We aimed to identify the disease-causing mutations in the triple-negative cases of ET and PMF by applying whole-exome sequencing (WES) on paired tumor and controlsamples from8 patients.Wefound evidence of clonal hematopoiesis in 5 of 8 studied cases based on clonality analysis and presence of somatic genetic aberrations. WES identified somatic mutations in 3 of 8 cases. We did not detect any novel recurrent somatic mutations. In 3 patientswith clonal hematopoiesis analyzed byWES, we identified a somatic MPL-S204P, a germline MPL-V285E mutation, and a germline JAK2-G571S variant. We performed Sanger sequencing of the entire coding region of MPL in 62, and of JAK2 in 49 additional triple-negative cases of ET or PMF. New somatic (T119I, S204F, E230G, Y591D) and 1germline(R321W)MPLmutationweredetected.All of theidentifiedMPLmutationswere gain-of-functionwhenanalyzedin functionalassays. JAK2 variants were identified in 5 of 57 triple-negative cases analyzed by WES and Sanger sequencing combined.We could demonstrate that JAK2-V625F andJAK2-F556V are gain-of-function mutations. Our results suggest that triple-negative casesofETandPMFdo not represent a homogenous disease entity. Cases with polyclonal hematopoiesis might represent hereditary disorders.
ASJC Scopus subject areas
- Cell Biology