All eight patients highly suspected of reactive erythrocytosis due to traits such as renal artery stenosis (n = 1), IP and lung cancer (n = 1), COPD (n = 1), chronic heart failure (n = 1), SAS (n = 1), heavy smoking (n = 5), and severe obesity (n = 1) had normal EPO levels. The gene discussed is EPO; the disease is incontinentia pigmenti.