HLA-DRB1 and acquired polycythemia vera: In theDRB1*04 haplotypes, the association withDQA1*03:01-DQB1*03:02 seems secondary to theassociation with DRB1*04, as a result of high linkagedisequilibrium (LD): The alleles DRB1*04:01, 04:03 and04:05 (and other) also are inserted inDQA1*03:01-DQB1*03:02 haplotypes, but were notassociated with increased susceptibility to PV (e.g., Carcassi etal., 1999; Haase etal., 2015).