Autoreactivity against plakophilin-3 (PKP3) has been demonstrated by Lambert et al. in five PNP/PAMS (100%) sera and in one PV (25%) serum in a series that evaluated sera from five PNP, four PV, two PF, five bullous pemphigoid (BP), one cicatricial pemphigoid, and one linear IgA dermatosis (53). The gene discussed is PKP3; the disease is acquired polycythemia vera.