HLA-DRB1-DQB1 genotypes from 2,555 multiple sclerosis patients, protective-predisposing nature for haplotypes in the second column, OR values of the individual haplotype (ORha and ORhb), the genotypic value of OR expected under log-additivity model (ORgexp) and the observed one (ORgobs), values of alpha parameter of the additivity violation. This evidence concerns the gene HLA-DRB1 and multiple sclerosis.