COL21A1 and acquired polycythemia vera: The antigens that were recognized by the majority of PV patients were DR α chain of the class II major histocompatibility complex (MHC) encoded by the human leukocyte antigen (HLA)-DRA gene (45% PV patients), Dsc1 and Dsc3, respectively; 44% each), ATPase, Ca++ transporting, type 2C, member 1 (ATP2C1; 43%), plakophilin 3 (PKP3; 43%), M3 subtype of muscarinic acetylcholine receptor (AChR) (CHRM3; 42%), collagen a1, type XXI, (COL21A1; 42%), annexin A8-like 1 molecule (ANXA8L1; 42%), complement component 5a receptor 1 (CD88; 42%) and e subunit of nicotinic AChR (CHRNE; 41%) (55).