P1014: germinal jak2 molecular alterations in patients with idiopathic erythrocytosis.

Topic: 15. Myeloproliferative neoplasms - Biology & Translational Research Background: Absolute erythrocytosis is a clinical condition characterised by an increased red cells production, resulting in haemoglobin and haematocrit levels above the reference range. Polycythaemia vera (PV) is a primary acquired erythrocytosis characterized by the presence of the somatic mutation JAK2V617F in exon 14 (95% of cases) and, rarely, the gain-of-functions mutations in exon 12 of JAK2 (3%). Secondary acquired erythrocytosis occur due to appropriate or inappropriate production of erythropoietin. Rare congenital erythrocytosis forms are classified as primary when erythropoietin receptor gene (EPOR) is altered and secondary when the defects are presents in genes involved in the oxygen sensing pathway or in globin genes. In 70% of patients no cause is recognized and they are considered Idiopathic Erythrocytosis (IE). Aims: We searched in patients with IE possible new variants with a Next Generation Sequencing (NGS) custom panel. Methods: An ad hoc NGS panel comprehending genes known to cause erythrocytosis or genes belonging to iron metabolism was used to search germline molecular variants in 118 sporadic IE patients (M/F =101/17; mean age 53.7±17.2 years) in whom JAK2 somatic variants have been not found with Sanger method. The approach used for library preparation was multiplexing PCR and data were analysed using bioinformatics tools to obtain the variants. All NGS data obtained were confirmed by Sanger Sequencing. Results: Within the 118 patients evaluated, we found 11 patients (9,3%) carrying a germline variant of JAK2 (Table 1). These variants, located in different exons then those of somatic mutations V617F and in exon 12, are mainly of uncertain significance and are almost all not described in the literature. Nine of these patients arrived at our attention because recurrent observation of increased haemoglobin and haematocrit. All of them were asymptomatic, and none had altered leucocytes or platelets count, nor serum erythropoietin level. The remaining 2 females were evaluated because belonging to a complex family already published (Genes and Diseases in printing) and are mother and sister of a patient with erythrocytosis. Summary/Conclusion: In this study the use of NGS allowed the identification of 11 patients carrying not well thorough germline variants in the JAK2 gene. Patients have been previously investigated for JAK2 classic somatic variants that were not found. Among the NGS identified variants, only JAK2L393V has been previously described and it has been hypothesised that it may precede the acquisition of JAK2V617F mutation. The others are not yet described and, at present, we do not know if these variants are pathogenetic or not. Their biological significance needs to be studied and understood. NGS in our experience help in understanding idiopathic erythrocytosis causes, mainly because explore complete genes. In conclusion, in patients clinically diagnosed as IE but lacking of alterations in the known exons of gene involved in erythrocytosis, NGS could be useful and open new diagnostic scenarios allowing the research of variants in all exons of known genes in erythrocytosis.Keywords: Erythrocytosis, Polycythemia vera