The Roles of Calreticulin Mutations in Myeloproliferative Neoplasms

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The myeloproliferative neoplasms (MPNs) are clonal hematopoietic stem cell disorders and can be classified into "classic" and "atypical" MPNs. Classic MPNs usually exhibit terminal myeloid cell expansion in the peripheral blood and include polycythemia vera, essential thrombocythemia (ET), primary myelofibrosis and chronic myeloid leukemia. Calreticulin (CALR) mutations have recently been discovered in about 30% JAK2/MPL-unmutated myeloproliferative neoplasms (MPN), and have become an important clonal marker for the diagnosis of essential thrombocythemia (ET) and primary myelofibrosis. The first aim of this study is to develop a rapid and sensitive screening tool for the detection of CALR mutations. We successfully developed a high-resolution melting analysis (HRMA) with the CFX Connect real-time system to detect CALR exon 9 mutations in ET patients. The maximal sensitivity of our HRMA system in identifying both CALR type 1 and type 2 mutants from patients’ genomic DNA was 2.5%. Our HRMA has a false positive rate of 3% and no false negative. The second aim of this study is to evaluate the clinical and prognostic significance of CALR mutations and JAK2/CALR co-mutations in Taiwanese ET patients. We screened for CALR exon 9 alterations with HRMA followed by TA-cloning in 92 adult ET patients. We identified classic CALR indel mutations in 21 (22.8%) patients. CALR mutations were associated with younger age (p=0.025), higher platelet count (p