APOE and early-onset autosomal dominant Alzheimer disease: In both cases, all identified haplotypes are common, and one is associated with risk of the disease (APOE ɛ4 in Alzheimer's disease; AG in ALS), one is associated with protection from the disease (APOE ɛ2 in Alzheimer's disease; GG in ALS), and one is neutral (APOE ɛ3 in Alzheimer's disease; GA in ALS).