Reduction in anti-Dsg1 IgG levels post rituximab is known to be a better predictor of remission in PV than anti-Dsg3 level reduction (14), but the greater reduction in anti-Dsg1 levels we observed in anti-Dsg1 positive PV is intriguing and suggests different disease biology underlying anti-Dsg1 and anti-Dsg3 responses. The gene discussed is DSG1; the disease is acquired polycythemia vera.