While the strongest statistical evidence for association in this region is with variants in HLA-DRB124, fine mapping in this region suggests that a class I haplotype (spanning the HLA-A and HLA-B loci) and a class II haplotype (including variants in HLA-DRB1, HLA-DQA1, and HLA-DQB1) are more precise markers of AD risk. This evidence concerns the gene HLA-DRB1 and Alzheimer disease.