HLA-DRB1 and acquired polycythemia vera: For example, alleles of HLA-DR4 (DRB1*0402 and *0406 in Ashkenazi Jews9 and Asians,10,11 respectively) and DR14 (DRB1*1401 and *1405 in Europeans12,13 and Asians,10,14 respectively) confer strong susceptibility to PV in different ethnic populations.