Introduction: Differential diagnosis of polyglobulia/erythrocytosis which is caused by deregulated erythropoiesis with an overproduction of red blood cells resulting in elevated hemoglobin and hematocrit levels is a diagnostic challenge.
Case Report: A 31-year-old man was referred to us with a suspected diagnosis of polycythemia vera (a clonal myeloproliferative neoplasm) because of erythrocytosis. One year before, he suffered from an ischemic central retinal vein occlusion of unknown cause. Aspirin treatment was initiated. His mother was diagnosed with a JAK2V617F negative polycythemia vera years earlier and treated with phlebotomies as well as aspirin. Apart from erythrocytosis, laboratory analysis showed a normal white blood cell and platelet counts. The differential blood picture and lactate dehydrogenase were within the normal ranges. Molecular testing for BCR-ABL, JAK2V617F and Calreticulin gene mutations by PCR was negative. Bone marrow biopsy was normal without signs for a myeloproliferative neoplasm. As almost all patients with polycythemia vera carry the phenotype-driver mutation JAK2V617F, further genetic testing for congenital causes of erythrocytosis was conducted. Mutations in the EPO- receptor gene were not found, but a very rare heterozygous point mutation in the beta-globin-chain [exon 2 (c. 119A>C) leading to a change in codon 40 (CAG>CCG)] was detected by next generation sequencing. This rare variant belongs to the high oxygen affinity hemoglobinopathies leading to a reduction of oxygen supply in tissues and an increase in red cell production.
Conclusion: The diagnosis of a JAK2 mutation negative polycythemia vera must always be questioned and congenital causes of erythrocytosis excluded as the therapeutic and prognostic consequences are immense. Rare variants of hemoglobinopathies, particularly those with high oxygen affinity need to be excluded by molecular testing.