Erythrocytosis is a rare condition caused by an increase in the red blood cell mass, hematocrit and/or heamoglobin. While the disease can occur due to several diverse causes, it is mostly diagnosed as polycythemia vera, an acquired type of erythrocytosis. Polycythemia vera develops upon acquired nucleotide variants in the JAK2 gene, most commonly the V617F variant in exon 14 or multiple other nucleotide variants in exon 12. On the other hand, congenital predispositions for familial erythrocytosis are rare and overall, their genetic background is relatively heterogeneous. The role of the JAK2 gene in the development of familial erythrocytosis is for now still poorly understood. Many patients with suspected familial erythrocytosis (about 70 %) remain without an identified cause of the disease and are thus diagnosed as having erythrocytosis of unknown cause. The aim of the study was to verify whether germline variants of the JAK2 gene are present in selected cohort of patients with confirmed erythrocytosis of unknown cause and to optimise the PCR method for amplification of selected exon and intron regions of gene JAK2. We included two samples of patients from the same family and seven control samples of healthy individuals. Two previously detected variants by NGS analysis in JAK2 gene were confirmed, one in exon 13 (rs1362123436) and another in intron 19 (rs780797578). Both variants are heterozygous, but yet without any significant clinical relevance. In addition, new nucleotide variants were detected in intron 12 in both patients and in introns 18 and 24 in one patient. To evaluate the significance of the newly discovered nucleotide variants, further functional tests will need to be performed in the future.
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