HLA-DRB1 and multiple sclerosis: Genome-wide association studies (GWASs) greatly helped to elucidate MS genetic risk, revealing a highly polygenic architecture for the disease, with an ever-increasing number of common SNPs associated to risk: the recent large-scale study of the International Multiple Sclerosis Genetics Consortium (IMSGC) on more than 100,000 individuals provided robust evidence for association of 200 autosomal risk loci outside the HLA region, one locus on chromosome X and 31 HLA loci in addition to the well-known HLA-DRB1*15:01 (International Multiple Sclerosis Genetics Consortium, 2019).