Abstract: The disclosed invention relates to a diagnostic method for Alzheimer's disease based on genotyping the Alpha-2-Macroglobulin locus. A statistically significant correlation was found between inheritance of particular alleles of the Alpha-2-Macroglobulin gene and the occurrence of Alzheimer's disease. The diagnostic method involves the isolation of nucleic acid from an individual and subsequent genotyping by means such as sequencing or restriction fragment length polymorphism analysis. The invention also provides a means of genotype analysis through protein isotyping Alpha-2-Macroglobulin variant proteins. Finally, kits for nucleic acid analysis or protein analysis are taught.