Background. Idiopathic erythrocytosis is the term reserved for cases with unexplained origins of abnormally increased hemoglobin after initial investigation. Extensive molecular investigation of genes associated with oxygen sensing and erythropoietin signaling pathways, in those cases, usually involves sequencing all of their exons and it may be time consuming. Aim. To perform a strategy for molecular investigation of patients with idiopathic erythrocytosis regarding oxygen sensing and erythropoietin signaling pathways. Methods. Samples of patients with idiopathic erythrocytosis were evaluated for the EPOR, VHL, PHD2, and HIF-2α genes using bidirectional sequencing of their hotspots. Results. One case was associated with HIF-2α mutation. Sequencing did not identify any pathogenic mutation in 4 of 5 cases studied in any of the studied genes. Three known nonpathogenic polymorphisms were found (VHL p.P25L, rs35460768; HIF-2α p.N636N, rs35606117; HIF-2α p.P579P, rs184760160). Conclusion. Extensive molecular investigation of cases considered as idiopathic erythrocytosis does not frequently change the treatment of the patient. However, we propose a complementary molecular investigation of those cases comprising genes associated with erythrocytosis phenotype to meet both academic and genetic counseling purposes. 1. Introduction Absolute erythrocytosis should be suspected when hemoglobin (Hb) is greater than 16.5？g/dL in females or 18.0？g/dL in males [1] and defines a status of elevated hemoglobin. Causes of erythrocytosis can be divided into two groups: primary, in which there is an intrinsic problem in bone marrow driving abnormal erythropoiesis, or secondary, in which there is an event outside bone marrow leading to an abnormal production of erythrocytes [1]. Both groups can be further classified into acquired or congenital. Within the group of primary erythrocytosis, erythropoietin receptor (EPOR) mutation (congenital) and polycythemia vera (PV, acquired) stand out. Within the group of secondary erythrocytosis, there are multiple acquired causes (hypoxia, EPO pathologic production, and drugs) and a restricted subgroup of congenital causes (VHL, PHD2, and HIF-2α mutations; high oxygen-affinity hemoglobin; and bisphosphoglycerate mutase deficiency) (Figure 1) [1–3]. Figure 1: Representation of diagnostic strategy for patients with erythrocytosis without acquired secondary causes. The most common example of primary erythrocytosis is polycythemia vera (PV). Notably, the majority of idiopathic erythrocytosis patients cannot be classified into the OMIM
References
[1]
F. S. Lee and M. J. Percy, “The HIF pathway and erythrocytosis,” Annual Review of Pathology: Mechanisms of Disease, vol. 6, pp. 165–192, 2011.
[2]
M. F. McMullin, “The classification and diagnosis of erythrocytosis,” International Journal of Laboratory Hematology, vol. 30, no. 6, pp. 447–459, 2008.
[3]
D. J. Weatherall, “Polycythemia resulting from abnormal hemoglobins,” The New England Journal of Medicine, vol. 280, no. 11, pp. 604–606, 1969.
[4]
M. J. Percy, P. A. Beer, G. Campbell et al., “Novel exon 12 mutations in the HIF2A gene associated with erythrocytosis,” Blood, vol. 111, no. 11, pp. 5400–5402, 2008.
[5]
M. J. Percy, P. W. Furlow, P. A. Beer, T. R. J. Lappin, M. F. McMullin, and F. S. Lee, “A novel erythrocytosis-associated PHD2 mutation suggests the location of a HIF binding groove,” Blood, vol. 110, no. 6, pp. 2193–2196, 2007.
[6]
M. J. Percy, Y. J. Chung, C. Harrison et al., “Two new mutations in the HIF2A gene associated with erythrocytosis,” American Journal of Hematology, vol. 87, no. 4, pp. 439–442, 2012.
[7]
M. J. Percy, L. M. Scott, W. N. Erber et al., “The frequency of JAK2 exon 12 mutations in idiopathic erythrocytosis patients with low serum erythropoietin levels,” Haematologica, vol. 92, no. 12, pp. 1607–1614, 2007.
[8]
R. H. Nussenzveig, T. Burjanivova, M. E. Salama, et al., “Detection of JAK2 mutations in paraffin marrow biopsies by high resolution melting analysis: identification of L611S alone and in cis with V617F in polycythemia vera,” Leukemia & Lymphoma, vol. 53, no. 12, pp. 2479–2486, 2012.
[9]
P. C. Junior Lima Santos, R. A. Gadi Soares, J. E. Krieger, E. M. Guerra-Shinohara, and A. C. Pereira, “Genotyping of the hemochromatosis HFE p.H63D and p.C282Y mutations by high-resolution melting with the Rotor-Gene 6000 instrument,” Clinical Chemistry and Laboratory Medicine, vol. 49, no. 10, pp. 1633–1636, 2011.
[10]
S. Carillo, L. Henry, E. Lippert et al., “Nested high-resolution melting curve analysis: a highly sensitive, reliable, and simple method for detection of Jak2 exon 12 mutations-clinical relevance in the monitoring of polycythemia,” Journal of Molecular Diagnostics, vol. 13, no. 3, pp. 263–270, 2011.
[11]
M. Al-Sheikh, E. Mazurier, B. Gardie et al., “A study of 36 unrelated cases with pure erythrocytosis revealed three new mutations in the erythropoietin receptor gene,” Haematologica, vol. 93, no. 7, pp. 1072–1075, 2008.
[12]
K. O'Rourke, D. J. Fairbairn, K. A. Jackson, K. L. Morris, S.-K. Tey, and G. A. Kennedy, “A novel mutation of the erythropoietin receptor gene associated with primary familial and congenital polycythaemia,” International Journal of Hematology, vol. 93, no. 4, pp. 542–544, 2011.
[13]
M. J. Percy, “Genetically heterogeneous origins of idiopathic erythrocytosis,” Hematology, vol. 12, no. 2, pp. 131–139, 2007.
[14]
H. Cario, M. F. McMullin, C. Bento, et al., “Erythrocytosis in children and adolescents-classification, characterization, and consensus recommendations for the diagnostic approach,” Pediatric Blood & Cancer, vol. 60, no. 11, pp. 1734–1738, 2013.
[15]
C. Bento, M. J. Percy, B. Gardie, et al., “Genetic basis of congenital erythrocytosis: mutation update and online databases,” Human Mutation, 2013.
[16]
K. Hussein, M. Percy, and M. F. McMullin, “Clinical utility gene card for: familial erythrocytosis,” European Journal of Human Genetics, vol. 20, no. 5, 2012.
[17]
E. R. Woodward, K. Wall, J. Forsyth, F. Macdonald, and E. R. Maher, “VHL mutation analysis in patients with isolated central nervous system haemangioblastoma,” Brain, vol. 130, part 3, pp. 836–842, 2007.
[18]
V. R. Gordeuk and J. T. Prchal, “Vascular complications in Chuvash polycythemia,” Seminars in Thrombosis and Hemostasis, vol. 32, no. 3, pp. 289–294, 2006.
[19]
V. R. Gordeuk, A. I. Sergueeva, G. Y. Miasnikova et al., “Congenital disorder of oxygen sensing: association of the homozygous Chuvash polycythemia VHL mutation with thrombosis and vascular abnormalities but not tumors,” Blood, vol. 103, no. 10, pp. 3924–3932, 2004.
