HLA-DRB1 and Cognitive impairment: Both have previously been associated with relapse risk in children, AHI1 directly influencing relapse risk25 and HLA-DRB1*1501 by modifying the association of vitamin D levels with relapse rate.26 While HLA-DRB1*1501 may be associated with earlier onset of cognitive impairment,17 we did not find an effect on 30-year cognitive outcomes.