Several SNPs in the FTO gene have been reported to be associated with obesity traits 12 (link)–14 (link). These SNPs are in strong linkage disequilibrium (LD). Of the three SNPs in FTO that were first reported to be associated with obesity (rs1421085, rs17817449, rs9939609) and subsequently replicated in several studies, we focused on rs1421085, an obesity-related FTO SNP that has previously been associated with common mental disorders as well as with brain atrophy in non-demented older individuals 15 (link), 16 (link). In the BLSA, we confirmed that the rs1421085 SNP was in high LD with both rs17817449 LD=0.927) as well as with rs9939609 (LD=0.931). Genome-wide genotyping was performed using the Illumina Infinium HumanHap550 genotyping chip (Illumina, San Diego, California), assaying >555,000 unique SNPs per sample. Standard quality control of genotyping data was conducted including verification of data completeness, Hardy-Weinberg equilibrium, and Mendelian incompatibilities as described previously 17 , 18 (link). We entered the number of obesity-related risk C alleles of rs1421085 (0,1 or 2) assuming additive models. In 15O-water PET analyses where dominant models were used because of small sample size, participants with one or two obesity-related risk C alleles of rs1421085 were classified as FTO+ whereas those with T/T genotype were classified as FTO−.