Sum scores were created using the --score option in PLINK v1.07 (Purcell et al., 2007). The number of risk alleles was added and then divided by the number of non-missing genotypes to create a normalized allele count for each individual. Because odds ratios associated with the risk alleles varied across family-based analyses in COGA and replication studies, an additive score was created without weighting alleles by effect size. The risk allele in the SAGE and COGA samples was determined by matching by frequency with alleles that were associated with AD in the family sample.
