HLA-DRB1 and Myalgia: Alleles of HLA-DRB1*04, particularly the HLA-DRB1*0401, DRB1*0404 or DRB1*0408 haplotypes, have been shown to be associated with the occurrence of GCA in independent cohorts [16,17,18,19,20,21,22,23,24,25,26,27] and are expressed by 60% of patients affected by polymyalgia rheumatica (PMR) or GCA [18,24,28].