On the one hand, the availability of active mouse models of PV and Atypical Pemphigus (DSC3) responds to those research needs, while on the other hand, no active mouse model of PF (DSG1) or Mucocutaneous Pemphigus, where autoantibodies target both DSG1 and DSG3, has been generated yet. The gene discussed is DSG1; the disease is acquired polycythemia vera.