Exploration of the Enteric Nervous System in Alzheimer Disease

The close homology between the central and enteric nervous system suggests that a disease process affecting the central nervous system could also involve its enteric counterpart. This has already been demonstrated for patients with Parkinson's disease but needs to be proven for Alzheimer's disease. Studies on enteric nervous system during Alzheimer's disease are indeed in low number and don't have led to definite conclusion. The investigators thus propose to realize a complete analysis of the enteric nervous systems in Alzheimer's disease by studying the presence of "tau' protein, of beta-amyloid peptide,... not only by immunohistochemical but also by a biochemical approach. This study will be realized from colonic samples.

Inclusion Criteria: * For the 3 groups of patients : colonoscopy planned by a gastroenterologist in the context ot the usual medical follow-up of the patient For patients with Alzheimer's disease : * Patient with early to moderate Alzheimer disease (continuum of patients with mild cognitive impairment due to Alzheimer's disease and patients diagnosed with probable Alzheimer's disease) according to the National Institute of Aging-Alzheimer's Association (NIA AA) criteria * Mini-Mental State Examination (MMSE) score ≥18; * Has one informant or care partner; * No parkinsonian syndrome * No sign of lewy Body dementia For patients with Parkinson's disease: * patients with Parkinson Disease according to the United Kingdom Parkinson's Disease Society Brain Bank (UKPDSBB) criteria * No dementia sign or cognitive deficit associated to Alzheimer's disease For patients without neurodegenerative disease: * No history or current neurological/degenerative condition (e.g, lewy body dementia, Parkinson's disease, Parkinsonian syndrome, Alzheimer's disease,…) * No memory complaint with a Mac Nair score ≤15 * MMSE score ≥28 ; * Patient at risk of colic cancer with a colonoscopy scheduled Exclusion Criteria: For the 3 groups of patients : : * History of colonic disorder ((e.g inflammatory condition, adenocarcinoma) * contra-indications to colonoscopy For patients with Alzheimer's disease and for patients with Parkinson's disease: \- Any neurological/neurodegenerative condition different from the group to which it belongs (e.g other than Alzheimer's disease for Alzheimer's disease group or other than Parkinson's disease for Parkinson's disease group….) For patients without neurodegenerative disease: * Any neurological/neurodegenerative condition (e.g lewy body dementia, Parkinsonian syndrome, Parkinson's disease, Alzheimer's disease..).. * functional colopathy