Studies by Olsson et al. and Hedstrom et al. suggest that the presence of high-risk HLA haplotypes, especially those containing DRB1*15:01 and lacking A*02:01, may intensify the negative correlations among childhood obesity, smoking, infectious mononucleosis, solvent exposure, and the likelihood of developing MS [251, 252]. This evidence concerns the gene HLA-DRB1 and infectious mononucleosis.