Abstract: Translocase of outer mitochondrial membrane 40 homolog (TOMM40) gene has been reported in several GWAS to be associated with Alzheimer disease (AD). Gene expression studies thus far only showed TOMM40 differential expression in one study on brain cortex and not in peripheral blood. We studied the gene expression profiles of AD blood versus controls in an Asian population in Singapore. In this first analysis we focused on genes that have been previously reported on GWAS. We found TOMM40 to be significantly down-regulated in blood samples of AD in one discovery and two validation sets, totalling 45 subjects (mean age 76.90, SD 6.46) and 45 controls (mean age 76.23, SD 5.09), matched for ethnicity and gender. The function of TOMM40 is not yet fully characterized but is believed to be involved in import and trafficking of protein into mitochondria. Therefore TOMM40 downregulation, found in the brain in severe AD and in our blood profile, may be a potential marker for AD, disease severity or progression and merit further investigation.