o5% and platelet counts are not elevated. By strictly adhering to the 2008 WHO criteria, we provide important molecular information in a relatively homogenous and well-defined group of patients. Morphological diagnoses are often subjective, with inter-observer variability, and inaccurate classification of myeloid neoplasms can result in erroneous estimation of associated molecular abnormalities. Specifically, it is important to note that BM ring sideroblasts are sometimes seen in both PMF and ET, and it is possible to misdiagnose some of these cases as RARS-T or RARS. 10,11 CONFLICT OF INTEREST The authors declare no conflict of interest. MM Patnaik, A Belachew, C Finke, TL Lasho, CA Hanson and A Tefferi Division of Hematology, Department of Medicine, Mayo Clinic, Rochester, MN, USA E-mail: tefferi.ayalew@mayo.edu REFERENCES 1 Klampfl T, Gisslinger H, Harutyunyan AS, Nivarthi H, Rumi E, Milosevic JD et al. Somatic mutations of calreticulin in myeloproliferative neoplasms. N Engl J Med 2013; 369: 2379–2390. 2 Nangalia J, Massie CE, Baxter EJ, Nice FL, Gundem G, Wedge DC et al. Somatic CALR mutations in myeloproliferative neoplasms with nonmutated JAK2. N Engl J Med 2013; 369: 2391–2405. 3 Tefferi A, Lasho TL, Finke CM, Knudson RA, Ketterling R, Hanson CH et al. CALR vs JAK2 vs MPL mutated or triple-negative myelofibrosis: clinical, cytogenetic and molecular comparisons. Leukemia 2014; e-pub ahead of print 9 January 2014, doi:10.1038/leu.2014.3. 4 Rotunno G, Mannarelli C, Guglielmelli P, Pacilli A, Pancrazzi A, Pieri L et al. Impact of calreticulin mutations on clinical and hematological phenotype and outcome in essential thrombocythemia. Blood 2013; e-pub ahead of print 26 December 2013. 5 Patnaik MM, Hanson CA, Sulai NH, Hodnefield JM, Knudson RA, Ketterling RP et al. Prognostic irrelevance of ring sideroblast percentage in World Health Organization-defined myelodysplastic syndromes without excess blasts. Blood 2012; 119: 5674–5677. 6 Patnaik MM, Lasho TL, Hodnefield JM, Knudson RA, Ketterling RP, Garcia-Manero G et al. SF3B1 mutations are prevalent in myelodysplastic syndromes with ring sideroblasts but do not hold independent prognostic value. Blood 2012; 119: 569–572. 7 Swederlow S, Campo E, Harris NL, Jaffe ES, Pileri SA, Stein H et al. WHO Classifi- cation of Tumors of Haematopoietic and Lymphoid Tissues. IARC: Lyon, France, 2008. 8 Patnaik MM, Hanson CA, Hodnefield JM, Lasho TL, Finke CM, Knudson RA et al. Differential prognostic effect of IDH1 versus IDH2 mutations in myelodysplastic syndromes: a Mayo Clinic study of 277 patients. Leukemia 2012; 26: 101–105. 9 Patnaik MM, Lasho TL, Finke CM, Hanson CA, Hodnefield JM, Knudson RA et al. Spliceosome mutations involving SRSF2, SF3B1, and U2AF35 in chronic myelomonocytic leukemia: prevalence, clinical correlates, and prognostic relevance. Am J Hematol 2013; 88: 201–206. 10 Schmitt-Graeff A, Thiele J, Zuk I, Kvasnicka HM. Essential thrombocythemia with ringed sideroblasts: a heterogeneous spectrum of diseases, but not a distinct entity. Haematologica 2002; 87: 392–399. 11 Lasho TL, Finke CM, Hanson CA, Jimma T, Knudson RA, Ketterling RP et al. SF3B1 mutations in primary myelofibrosis: clinical, histopathology and genetic correlates among 155 patients. Leukemia 2012; 26: 1135–1137. OPEN The germline sequence variant rs2736100_C in TERT associates with myeloproliferative neoplasms Leukemia (2014) 28, 1371–1374; doi:10.1038/leu.2014.48 Myeloproliferative neoplasms (MPN) constitute a group of clonal hematological disorders characterized by an expansion and accumulation of one or more mature cell types of the myeloid lineages. There are four main groups of MPNs that can be classified by the presence or absence of the Philadelphia (Ph) chromosome. 1 Chronic myeloid leukemia is accompanied by the Ph chromosome, whereas polycythemia vera (PV), essential thrombocythemia (ET) and primary myelofibrosis (PMF) are not. 1 In all three Ph-negative MPN subtypes (hereafter called MPN), a recurrent somatic mutation is frequently found in the pseudokinase region of Janus kinase 2 (JAK2 V617F ). 2 The mutation is observed in about 80–95% of PV cases, 50% of ET cases and 60% of PMF cases. 2 Owing to the activating nature of the mutation, it leads to constant stimulation of myeloid proliferation. 2 Family studies have shown that germline variants may predispose to the disease as the risk of MPN among first- degree relatives of MPN patients in Sweden is five to sevenfold greater than that in the general population. 2 Furthermore, common germline single-nucleotide polymorphisms (SNPs) at the JAK2 locus have been associated with MPN. 3–5 The aim of the current study was to search for germline sequence variants that associate with risk of MPNs by performing genome-wide association analysis. For the association analysis, we used sequence variants identified by whole genome sequencing (WGS), to an average depth of 22  , of DNA isolated from white blood cells of 2230 Icelanders (Supplementary Material). Using imputation assisted by long-range haplotype phasing, the genotype probabilities of all the 34.2 million sequence variants identified were determined for Icelanders genotyped with Illumina (San Diego, CA, USA) SNP chips. Furthermore, using Icelandic genealogical information, genotype probabilities were calculated for individuals who are close relatives of chip-typed individuals (familial imputation) (Supplementary Material). We then tested the identified variants for association with MPN, using 237 Icelanders diagnosed with MPN, including PV (n ¼ 98), ET (n ¼ 40), PMF (n ¼ 26) and 34 128 Icelandic controls with imputed genotypes (Table 1 and Supplementary Table S1). It is worth stressing that somatic MPN mutations do not affect the association analysis as the variants identified through WGS and subsequently imputed into MPN cases are almost exclusively from individuals not diagnosed with MPN (one MPN case, diagnosed 9 years after blood draw, among the 2230 sequenced individuals). Assuming a multiplicative model, we observed a genome-wide significant association between MPN in the Icelandic population Accepted article preview online 30 January 2014; advance online publication, 21 February 2014 Letters to the Editor 1371 & 2014 Macmillan Publishers Limited Leukemia (2014) 1341 – 1379