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The polycythaemias 

The polycythaemias
The polycythaemias

Daniel Aruch

, and Ronald Hoffman

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date: 27 February 2021

Polycythaemia or erythrocytosis is characterized by an abnormal increase in the numbers of red blood cells, leading to an elevation in the haemoglobin concentration and haematocrit (>49% in men and >48% in women). The cause may be either (1) primary—due to an intrinsic defect of haematopoietic stem cells; or (2) secondary—due to extrinsic stimulation of progenitor erythroid cells by circulating growth factors; and the condition needs to be distinguished from (3) pseudopolycythaemia—in which haematocrit is raised because the plasma volume is decreased. Secondary polycythaemias: associated with appropriate erythropoietin secretion—conditions that are ultimately the result of tissue hypoxia and subsequent excessive erythropoietin production include (1) living at high altitude, (2) chronic lung disease, (3) cyanotic congenital heart disease with right-to-left shunting, (4) carbon monoxide intoxication—as occurs in heavy smokers, (5) haemoglobin variants with increased oxygen affinity, and (6) mutations in genes involved in the oxygen sensing pathway. Associated with inappropriate erythropoietin secretion—in the absence of tissue hypoxia, inappropriate erythropoietin production commonly originates from the kidney and many renal disorders are associated with erythrocytosis. Tumour-associated polycythaemia may also result from cerebellar haemangioblastoma, hepatocellular carcinoma, phaeochromocytoma, and other adrenal tumours. Primary polycythaemia: polycythaemia vera—is a clonal, chronic progressive haematological malignancy characterized by excessive proliferation of erythroid, myeloid, and megakaryocytic elements in the bone marrow. Aetiology—up to 95% of cases are caused by somatic mutations in the pluripotent haemopoietic stem cells leading to replacement of a key valine residue by phenylalanine at position 617 of the JAK2 kinase (V617F), which releases it from autoinhibition. Less common mutations have been described recently, primarily JAK2 exon 12 and LNK mutations.

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