GSTM1 and pulmonary hypertension: The hallmark characteristics of CMS are accentuated hypoxemia, excessive erythrocytosis (women: Hb ≥ 190 g/L, men: Hb ≥ 210 g/L), and pulmonary hypertension, which often results in right ventricular enlargement and hypertrophy, and in the later disease stage, leads to chronic heart failure.