Identficação de variantes no ÉXON 09 do gene calreticulina (CALR) em pacientes com trombocitemia essencial e mielofibrose

Abstract

BCR::ABL1 negative myeloproliferative neoplasms are hematological changes with clonal proliferative characteristics that affect one or more lineages of the myeloid group, including essential thrombocythemia and myelofibrosis. Showing proliferative characteristics in the production of megakaryocytes, leukocytes, platelets and with similar clinical evolution and changes in signaling pathways, mainly in the JAK-STAT pathway. The presence of variations in the CALR gene modifies the structural and functional formation of the Calreticulin protein, compromising cell proliferative normalities in essential thrombocythemia and myelofibrosis. CALR gene variants are in the region of exon 09 and are of the fifty-two base pair deletion (type 1) and or five base pair insertion (type 2) type. Modifying the base reading composition and giving rise to the formation of a new structural C-terminus of the protein, which contributes to distinct clinical pictures of essential thrombocythemia and myelofibrosis. Objective: To track changes in exon 09 of the CALR gene in patients with essential thrombocythemia and myelofibrosis. Methodology: 69 individuals clinically diagnosed with essential thrombocythemia (n=61) and myelofibrosis (n=8) were included in the study. Laboratory data were obtained from sample collections during the individuals' follow-up. Molecular evaluation was performed using Polymerase Chain Reaction and Sanger Sequencing to detect variants in the exon 09 region of the CALR gene. Results: in exon 09 of the CALR gene, the variants rs1555760738 (type 1) and rs765476509 (type 2) were identified. Of the patients with TE (n=61), 4 had it (type 1) and 10 had it (type2), while in MF (n=8), 2 variants were identified; one with type 1 and another with type 2. At the distribution level, there was a predominance of TE CALR type 2. In the analysis between TE subtypes, patients with type 2, presenting higher platelet counts and discreet changes in the clinical-laboratory profile in the other investigated. For patients with MF, the analysis was descriptive, consisting of a CALR type 1 individual (heterozygous) and a CALR type 2 individual (homozygous) presenting laboratory behavioral differences in both, mainly in platelet production. Conclusion: In the analysis between TE subtypes, patients with type 2 confirmed the association with the essential thrombocythemia phenotype and the high production of platelets. Regarding individuals with MF, which includes a rarely reported homozygosity, the association with clinical-laboratory behavior should be further evaluated. These findings confirm that frameshift modifications generated by CALR variants alter the structure of the C-domain of the calreticulin protein, which is involved in intermolecular processes and a constitutive activation in megakaryocyte formation.