The HLA gene variants within MHC class I and II regions associated with cognitive decline in Alzheimer’s disease (AD) include HLA class I genes (HLA-A2, HLA-A1, HLA-A24, HLA-B*4402, HFE H63D, HFE C282Y), HLA class II genes (HLA-DQB1*06 (HLA-DQ), rs9271192, HLA-DRB1*15, HLA-DRB1*04, HLA-DR15 haplotype (HLA-DR)), and TAP2 SNP rs241448 [38]. Here, HLA-DRB1 is linked to early-onset autosomal dominant Alzheimer disease.