Alzheimer's disease (AD) is the leading cause of dementia in France. It is a multifactorial pathology, combining genetic and environmental risk factors. Homocysteine, a sulfur-containing amino acid belonging to the methionine-monocarbon cycle, has frequently been found at high levels in neurodegenerative diseases, and in AD in particular. It has been shown on human brain sections that the interaction of homocysteine with tau and MAP1, two key AD proteins, was significantly higher in AD patients than in controls, and corresponded to an N-homocysteinylation type interaction.

This is a prospective study, the main objective of which is to compare MAP1 N-homocysteinylation levels in fibroblasts from individuals with AD versus disease-free cell lines.

Inclusion Criteria:

• age > 18 years
• Age of onset of AD < 75 years
• Person with AD with positive CSF biomarkers
• Person who has previously benefited from an analysis of AD genetic characteristics (APP, PSEN1, PSEN2, TREM2, ABCA7, SORL1 genes and ApoE status) and an analysis of monocarbon metabolism genes in the case of biochemical abnormalities by clinical exome, targeted panel or complete exome, and for whom the data set is already available.

Exclusion Criteria:

• Pregnant, parturient or breast-feeding women
• Minor (not emancipated)
• Person of legal age (subject to a legal protection measure)
• Adult unable to give consent