In pemphigus vulgaris (PV), IgG autoantibodies against Dsg3 cause a profound blistering of the skin and mucosal epithelia, whereas in pemphigus foliaceus, IgG autoantibodies against Dsg1 cause a blistering phenotype restricted to the skin (for a review, see9, 10). The gene discussed is DSG3; the disease is acquired polycythemia vera.