Myeloproliferative neoplasms (MPN), characterized by abnormal proliferation of myeloid series, were found to have specific molecular markers.1–5 In Philadelphia-negative and BCR-ABL-negative patients, JAK2 V617F mutation is the major marker and is present in approximately 90% in polycythemia vera patients and about 50~60% of patients with essential thrombocythemia (ET) and primary myelofibrosis (MF) patients.1–4 The identification of this mutation contributes to the diagnosis and prognostic significance, as reported in many articles.1–4 More recently, several investigations identified novel somatic mutations at the exon 9 of calreticulin (CALR) gene in 50~80% of JAK2V617F-negative ET and MF patients.5

CALR is a highly conserved endoplasmic reticulum calcium-binding chaperone that is related to calcium homeostasis, cell adhesion, and immune response.9 Until now, all CALR mutations have been found at exon 9, which encodes the C-domain region where there is a domain for Ca2+ to bind.5–9,14,15 Of the more than 50 mutations found, all were exclusively on JAK2 V617F-negative patients. Most of the mutations correspond to a 52 kb deletion (del 1092–1143, type 1) or a 5bp insertion (1151 ins TTGTC, type 2), resulting in premature terminations from these frameshift mutations.7,8 From previous studies, the CALR mutations had a unique clinical presentation compared with JAK2 V617F mutation; therefore, it is essential to survey these mutations in Philadelphia chromosome and/or BCR-ABL negative MPNs.10–14

High resolution melting (HRM) method using the saturating dsDNA binding dye for melting curve analysis is a rapid and labor-saving method for mutation screening.15 In this study, we used the HRM method to screen for these mutations in our ET patients by distinguishing the specific curve types. We also reviewed the clinical presentations of patients to find the relationship between mutations and clinical phenotypes.