Identifying calreticulin mutation status in JAK2 and MPL mutation negative patients with essential thrombocytosis and primary myelofibrosis

The myeloproliferative neoplasms are chronic myeloid cancers characterized by the overproduction of mature and immature blood cells. Essential trombocythemia (ET) and primary myelofibrosis (PMF) are two of the BCR-ABL negative chronic myeloproliferative neoplasms. JAK2 and MPL mutations are being used for the diagnosis of ET and PMF, but 30-40% of the patients do not carry any mutations at these genes. Recently, another gene called Calreticulin is thought to be involved in the development of ET and PMF. In this study, we investigated the CALR mutation frequency, mutation types and their relevance with clinical findings. 16 ET and 4 PMF patients were enrolled in this study. All patients were negative for JAK2V617F, MPL W515K/L and S505N mutations. We investigated CALR mutation status with sanger sequencing method. The mutation rate was 25% in general. However, we did not find any mutations in patients with PMF. We detected three different mutations (31.25%) in 5 patients with ET. Three of the mutations were 52 base pairs (bp) deletion (Type I mutation, c.1092_1143del), one was 5 bp insertion (Type II mutation, c.1154_1155insTTGTC) and the last one was 46 bp deletion (c.1094_1139del). All patients with Type I mutation were women and the mean age (23.3y) was found to be significantly lower compared to all groups (p=0.003). The results of the study showed us that the mutation rate and mutation types were similar with the previous studies. New prospective studies with larger cohort will help us to understand the effect of CALR mutations in the development and prognosis of myeloproliferative neoplasms.