The close homology between the central and enteric nervous systems suggests that a disease process affecting the central nervous system could also involve its enteric counterpart. The investigators have recently shown in that the enteric neurons can be readily analyzed using routine colonic biopsies. This led us to propose that the enteric nervous system could represent a unique window to assess the neuropathology in living patients with a neurodegenerative disorder. The investigators have already used this approach to show that Parkinson's disease pathology was recapitulated in a single colonic biopsy. By contrast to Parkinson's disease, the detection of Alzheimer's disease (AD) pathology in the enteric neurons has so far failed. This may be due to the low number of human tissue samples in addition to the low sensitivity of the immunohistochemical methods that were used. The aim of the current research project will be therefore to reevaluate AD pathology in a large number of human colonic samples using both a morphological and biochemical approach .

The enteric nervous system could represent a unique window to assess the neuropathology in living patients with AD. This might open the way to the development of novel AD biomarkers that will directly assess the neuropathological process.

Main Aim : To Analyze the presence of beta-amyloid pathology in the enteric nervous system (ENS) in AD patients

Secondary Aim(s):

1. To analyze and describe the presence of tau in the enteric nervous system (ENS) in AD patients
2. To assess neuronal loss in submucosal tissue in AD patients.
3. To examine Glia cells in the enteric nervous system in AD patients..

Inclusion Criteria:

- AD group : Patient with early to moderate Alzheimer disease (continuum of patients with MCI due to AD and patients diagnosed with probable AD) according to NIA NAA criteria MMSE score ≥18; Has one informant or care partner; No parkinsonian syndrome No sign of lewy Body dementia

- PD group (control group 1) : Patients with Parkinson Disease according UKPDSBB criteria, No dementia sign or cognitive deficit associated to AD

- PSP group (control group 2): Patients with possible or probable Progressive supranuclear palsy group PSP according to NINDS criteria Has one informant or care partner;

- Patient eligible for colorectal cancer screening (control group 3) : No history or current neurological/degenerative condition (e.g, lewy body dementia, PD, Parkinsonian syndrome, AD…) 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 all groups: History of colonic disorder (e.g inflammatory condition, adenocarcinoma) History of bleeding disorder Traitement anticoagulant ou antiagrégant en cours Treatment with anticoagulant or Platelet aggregation inhibiting drugs

- Patient with AD, PSP, PD: Any neurological/neurodegenerative condition different from the group to which it belongs (e.g other than AD for AD group or other than PD for PD group….)

- Patient eligible for colorectal cancer screening Any neurological/neurodegenerative condition (e.g lewy body dementia, Parkinsonian syndrome, PD, AD..)..

Functional colopathy or Irritable Bowel Syndrome