GSTM1 and acquired polycythemia vera: At sea level, other causes of polycythaemia, such as myeloproliferative diseases (polycythaemia vera), Chuvash polycythaemia and secondary polycythaemia, have been associated with an increased risk of thrombosis (Gordeuk et al., 2019; Nguyen et al., 2021), albeit this risk was not necessarily associated with increasing [Hb] (Gordeuk et al., 2019, 2020).