X-Linked Clonality Analysis and Quantitative JAK2V617F Assessment Reveals a Strong Association between Clonality and JAK2V617F in PV but Not in ET/MMM, and Identifies a Subset of JAK2V617F Negative ET and MMM Patients with Clonal Hematopoiesis.

Polycythemia vera (PV), essential thrombocythemia (ET), and myeloid metaplasia with myelofibrosis (MMM) are categorized as a set of phenotypically related myeloproliferative disorders (MPD). Recent work has identified a somatic mutation in the JAK2 tyrosine kinase (JAK2V617F) in the majority of PV and in a subset of ET and MMM. As most, but not all, patients with MPD have clonal granulocytes, we sought to determine if there was a relationship between granulocyte clonality and JAK2V617F mutational status using a quantitative clonality assay for the human androgen receptor gene (HUMARA) and a quantitative real-time PCR assay for JAK2V617F. 168 of 190 female MPD patients were informative for the HUMARA polymorphism, and 121 patients (72%) had allele skewing consistent with clonal granulopoiesis including 80% of MMM, 75% of PV, and 67% of ET. The quantitative real-time PCR assay for JAK2V617F detected the JAK2V617F allele in 98.8% of PV, 69% of ET, and 33% of MMM, and was more sensitive than direct sequencing. A significant correlation between the degree of allele skewing and quantitative JAK2V617F allelic ratio was observed in PV (p<0.0001) but not in ET (p= 0.2) or MMM (p=0.771). In addition, a subset of patients with ET and MMM with clonal granulocytes had JAK2V617F present in some, but not all, clonal granulocytes. These data suggest acquisition of the JAK2V617F mutation may be sufficient for the development of PV, but additional genetic events are necessary to cooperate with JAK2V617F in ET and MMM. Most importantly, we identified a subset of patients with ET (23%) and MMM (17%), but not PV, with clonal granulocytes who were JAK2V617F negative. A high-throughput screen for novel activating mutations in signal transduction pathways in JAK2V617F negative ET and MMM is warranted.