APOE and Alzheimer disease: The two-SNP haplotype that was most strongly associated with ALS in the joint analysis (rs3849942-rs10122902) mimics the behaviour of the APOE association with Alzheimer's disease; the three APOE alleles—ɛ2, ɛ3, and ɛ4—are in fact pairs of alleles at two SNPs forming a haplotype.