The Alzheimer's Disease Patient Registry (ADPR), consisting of 300 case and 450 control subjects residing in Olmstead County, Minnesota collected by Mayo Clinic physicians is potentially a rich resource for genome-wide linkage disequilibrium (LD) mapping of genes involved in Alzheimer's Disease (AD). Because of the demographic characteristics of the county (this population is mostly made up of individuals of Scandinavian descent), this population is rather homogeneous and therefore ideal for using LD methods to identify risk variants. We plan on using both pair-wise and multipoint LD methods to define the risk allele(s) within the previously identified late-onset AD candidate gene-containing loci (focusing on the Chromosome 9p22.1 locus first). To reduce the risk of false positive results from the analysis, examination of ADPR population homogeneity at a genetic level will be performed.