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

Females 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 = 0.009). The frequency of abnormalities of PRV-1, EEC, or Mpl was similar in monoclonal and polyclonal subjects (respectively, 28\%, 48\%, 75\%, and 37\%, 27\%, 63\%), and none of them correlated with thrombosis. We conclude that the exploited epigenetic markers constitute independent phenotypic variations and are not clustered according to monoclonality of myelopoiesis in ET; none of them could serve as a surrogate marker of thrombotic risk in male subjects with ET.