Down syndrome results from the trisomy of human chromosome 21 and is the most prevalent genetic cause of intellectual disability. Down syndrome results in various developmental changes that can be observed on a cellular level, including a change in the expression of certain proteins. Because receptor for activated C kinase 1 (RACK1) and amyloid precursor protein (APP) have both been implicated in the pathogenesis of Down syndrome and play a role in cell adhesion and motility, we hypothesized that their expression may vary in Down syndrome. Fibroblasts were obtained from a human diagnosed by karyotype for Down syndrome and a healthy human subject that was age, sex and race matched to the individual with Down syndrome. RACK1 and APP expression in these fibroblasts were labeled using quantitative immunocytochemistry. Preliminary results demonstrate that both RACK1 and APP are overexpressed in Down syndrome fibroblasts. Thus, it is likely that the overexpression of APP and RACK1 in Down syndrome may lead to inappropriate cell adhesion and motility, and contribute to the pathogenesis of this disorder. In future experiments, we will examine how RACK1 mRNA localization may be dysregulated in Down syndrome. In addition, the expression of APP and RACK1 in Down syndrome neurons, instead of fibroblasts, will be examined to further understand how these proteins contribute to the formation of brain connectivity. These experiments will further advance the understanding of Down syndrome, its connection to Alzheimer's disease, and aid in the development of treatments for these disorders.