The decrease in c-Fos expression with aging and its increased expression in Alzheimer’s disease and other neurological disorders suggest that the AP-1 dimer, formed by c-Fos, may be critical in the upregulation of gene transcription involved in pathways detrimental to neuronal function, such as inflammation and reactive oxygen species, ultimately leading to neuronal dysfunction and even neuronal death. The gene discussed is JUN; the disease is Alzheimer disease.