A total of 302 community-dwelling patients with severe dementia, Alzheimer’s disease, with or without a coexisting diagnosis of vascular dementia, and a score of 10 or less on the Mini-Mental State Examination who received previous treatment with a cholinesterase inhibitor (with or without memantine) for at least 3 months, will be randomized to continue or discontinue drug treatment. This evidence concerns the gene BCHE and Alzheimer disease.