PRV‐1, erythroid colonies and platelet Mpl are unrelated to thrombosis in essential thrombocythaemia

Abstract

PRV-1, erythroid colonies and platelet Mpl are unrelated to thrombosis in essential thrombocythaemiaAn increased incidence of thrombosis, both arterial and venous, has been reported in essential thrombocythaemia (ET) (Spivak et al, 2003). ET is considered as a 'clonal' myeloproliferative disorder, but studies of X-chromosome inactivation pattern (XCIP) indicated that a proportion of patients with ET, diagnosed according to the currently available criteria, presented polyclonal myelopoiesis (el-Kassar et al, 1997;Harrison et al, 1999a;Chiusolo et al, 2001;Shih et al, 2001Shih et al, , 2002. Since the rate of thrombosis in patients with polyclonal myelopoiesis was significantly lower than in monoclonal patients (Harrison et al, 1999a;Chiusolo et al, 2001;Shih et al, 2002), assessment of clonality would enable the identification of patients within different risk categories suitable for risk-adapted treatment strategies . However, beyond concerns as a result of age-dependent unbalanced X-chromosome skewing (Champion et al, 1997;Mitterbauer et al, 1999), the major limitation of XCIP analysis is that it can be performed only in women.No specific molecular marker of ET has been identified yet, although a number of cellular and molecular abnormalities have been described (Spivak et al, 2003); these include reduced platelet content of Mpl, the receptor for thrombopoietin (Horikawa et al, 1997;Harrison et al, 1999b;Li et al, 2000), spontaneous in vitro growth of erythroid progenitors (endogenous erythroid colonies, EEC) (Prchal & Axelrad, 1974;Kralovics et al, 2003) and overexpression of the PRV-1 gene (Teofili et al, 2002a;Johansson et al, 2003a;Liu et al, 2003;Tefferi et al, 2004). However, an association between these abnormalities and thrombosis has been reported only occasionally (Teofili et al, 2002b;Johansson et al, 2003b).The aim of this study was to assess whether any of these three epigenetic markers clustered with clonality status in females with ET; if so, it (they) might be considered to represent (a) 'surrogate marker(s)' of clonality and, possibly, of thrombotic risk. Patients and methodsOne hundred females with ET were studied; they comprised an unselected consecutive population of patients who attended the outpatient departments of our Haematology institutions for either diagnostic or routine follow-up purposes. Diagnosis SummaryFemales with the monoclonal type of essential thrombocythaemia (ET), based on the X-chromosome inactivation pattern (XCIP), have previously been shown to present a higher incidence of thrombosis than polyclonal ones. We aimed to assess correlations between XCIP, thrombosis, and three epigenetic markers of ET, namely PRV-1 overexpression, endogenous erythroid colony (EEC) formation, and reduced platelet Mpl content. Fifty-three (60%) of 88 subjects studied had monoclonal myelopoiesis and presented a 32% incidence of major thrombosis compared with 6% of polyclonal subjects (P ¼ 0AE009). The frequency of abnormalities of PRV-1, EEC, or Mpl was similar in monoclonal and polyclonal su...

Clinical implications of the JAK2 V617F mutation in essential thrombocythemia

“…On the contrary, there was a correlation between major thromboses and XCIP clonality in female patients (P ¼ 0.038), as reported. 8 Patients with JAK2 mutation had a higher frequency of EEC (55 vs 38%) and PRV-1 overexpression (40 vs 33%) and, on the other hand, less frequently reduced c-Mpl platelet content (66 vs 81%), but none of these differences was statistically significant. The percentage of subjects with clonal hemopoiesis was identical in the two groups (66%); the findings of JAK2 mutation in females with a polyclonal pattern of hematopoiesis, based on the XCIP analysis, was not unexpected, since the allele-specific PCR strategy used for the detection of mutated JAK2 alleles has a sensitivity of as few as 3% of nucleated cells, 2 as compared to an at least 75% clonal allele predominance that is required for the definition of clonality with the HUMARA assay.…”

“…8 Search for JAK2 mutation was performed by an allele-specific PCR, starting from 75 ng DNA purified from granulocytes. 2 To evaluate whether the mutation was carried in the homozygous or heterozygous state, digestion of PCR products with BsaXI restriction enzyme (New England Biolabs, Hitchin, UK) was performed as described.…”

Pulmonary hypertension in patients with chronic myeloproliferative disorders

“…Spontaneous EEC formation may be associated with thrombosis, particularly of hepatic veins, in the absence of other peripheral blood abnormalities and the presence of EEC leads to the diagnosis of primary myeloproliferative disorder in 78% of cases with apparent idiopathic Budd-Chiari syndrome, and in about half of patients with portal, splenic and/or mesenteric vein thrombosis [38,39]. Another study did not find EEC as a surrogate marker of thrombotic risk (not specifically related to the splanchnic vessels) in male subjects with essential thrombocytosis [40]. In the study of GUILPAIN et al [14] the diagnosis of CTEPH ( fig.…”

Influence of JAK2V617F allele burden on phenotype in essential thrombocythemia

“…XCIP evaluation was performed at the HUMARA locus in female patients aged less than 60 years old using a PCR assay and enzymatic digestion with RsaI and HpaII, as described elsewhere. 26 Immunomagnetically purified CD3 + T-lymphocytes were used as control cells. V617F allele burden and hematologic parameters.…”