Alzheimer disease (AD) is the most common neurodegenerative dementia. It leads to a progressive loss of cognitive functions, especially memory. Most of AD cases are sporadic, resulting from the interplay of genetic and environmental factors which get involved in the regulation of the expression of thousands of genes, a mechanism called epigenetic[1]. Epigenetic modifications, by modifying genes transcription, help to orchestrate the phenotypical changes linked to development, aging or even diseases and cancer[2]. In AD, recent studies showed rapid, dynamic and persistent epigenetic mutations that are believed to have consequences on brain functions. One of the earliest biomarker of AD is amyloïd-beta deposition in the brain. According to current studies, deposition of amyloïd-beta begins approximately 20 years before the first symptoms linked to the disease, which questions us about what could have happened around or before that time. During this study, we tried to identify a possible correlation between the experiencing of a strong psychologically stressful life event, which could have lead to several epigenetic changes, and the occurrence of Mild Cognitive Impairment (MCI) or AD dozens of years later. We also tried to highlight a possible difference in the delay between MCI and AD patients.