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The JAK2 V617 F somatic mutation is present in the majority of patients with myeloproliferative cancer (polycythaemia vera, essential thrombocytosis, and primary myelofibrosis). However, the diagnostic value of the JAK2 V617 F somatic mutation for myeloproliferative cancer in the general population is unknown. We examined this question in 49 488 individuals from the Copenhagen General Population Study. We also examined the association between JAK2 V617 F somatic mutation, rs10974944 germline genotype, haematological phenotype, any cancer, haematological cancer, myeloproliferative cancer, ischaemic heart disease, and venous thromboembolism. The JAK2 V617 F somatic mutation was present in 0·1% ( n = 68), increasing across rs10974944 germline genotypes ( P-trend = 0·001). JAK2 V617 F somatic mutation positives versus negatives had higher erythrocyte ( P = 2 × 10−5), thrombocyte ( P = 2 × 10−16), and leucocyte ( P = 4 × 10−9) counts, and had 2·7-/2·5-fold risk of cancer (prevalent/incident), 44-/28-fold risk of haematological cancer, 221-/97-fold risk of myeloproliferative cancer, 2·2-/1·2-fold risk of ischaemic heart disease, and 3·1-/1·0-fold risk of venous thromboembolism. By combining conventional haematological parameters with a test for the JAK2 V617 F somatic mutation, myelo;?>proliferative cancer could be identified or ruled out with a sensitivity of 47-100% and a specificity of 98-100%. In conclusion, in the general population the JAK2 V617 F somatic mutation has a high diagnostic value for myeloproliferative cancer when combined with conventional haematological parameters. [ABSTRACT FROM AUTHOR]

Meta‐analyses and Mendelian randomization (MR) may clarify the associations of smoking, blood cells and myeloproliferative neoplasms (MPN). We investigated the association of smoking with blood cells in the Danish General Suburban Population Study (GESUS, n = 11 083), by meta‐analyses (including GESUS) of 92 studies (n = 531 741) and MR of smoking variant CHRNA3 (rs1051730[A]) in UK Biobank, and with MPN in a meta‐analysis of six studies (n (total/cases):1 425 529/2187), totalling 2 307 745 participants. In the meta‐analysis the random‐effects standardized mean difference (SMD) in current smokers versus non‐smokers was 0·82 (0·75–0·89, P = 2·0 * 10−108) for leukocytes, 0·09 (−0·02 to 0·21, P = 0·12) for erythrocytes, 0·53 (0·42–0·64, P = 8·0 * 10−22) for haematocrit, 0·42 (0·34–0·51, P = 7·1 * 10−21) for haemoglobin, 0·19 (0·08–0·31, P = 1·2 * 10−3) for mean corpuscular haemoglobin (MCH), 0·29 (0·19–0·39, P = 1·6 * 10−8) for mean corpuscular volume (MCV), and 0·04 (−0·04 to 0·13, P = 0·34) for platelets with trends for ever/ex‐/current smokers, light/heavy smokers and female/male smokers. Analyses presented high heterogeneity but low publication bias. Per allele in CHRNA3, cigarettes per day in current smokers was associated with increased blood cell counts (leukocytes, neutrophils), MCH, red cell distribution width (RDW) and MCV. The pooled fixed‐effects odds ratio for MPN was 1·44 [95% confidence interval (CI): 1·33–1·56; P = 1·8 * 10−19; I2 = 0%] in current smokers, 1·29 (1·15–1·44; P = 8·0 * 10−6; I2 = 0%) in ex‐smokers, 1·49 (1·26–1·77; P = 4·4 * 10−6; I2 = 0%) in light smokers and 2·04 (1·74–2·39, P = 2·3 * 10−18; I2 = 51%) in heavy smokers compared with non‐smokers. Smoking is observationally and genetically associated with increased leukocyte counts and red blood cell indices (MCH, MCV, RDW) and observationally with risk of MPN in current and ex‐smokers versus non/never‐smokers. [ABSTRACT FROM AUTHOR]