Patient description: An 89-year-old man was brought to the emergency department by his wife and son after six months of progressive changes in cognition and personality. He began to have poor memory, difficulty expressing himself, and exhibited unusual behaviors, such as pouring milk onto the table and undressing immediately after getting dressed. He is unable to dress, bathe, use the toilet, or walk independently. On examination the patient's temperature was 36.5C (97.7F), the heart rate 61 bpm in an irregular rhythm, the blood pressure 144/78 mm Hg, and the respiratory rate 18 bpm. The patient was alert and oriented to self and city but not year. He frequently interrupted the examiner. He repeatedly reached out to grab things in front of him, including the examiner's tie and face. He could not spell the word "world" backward, could not follow commands involving multiple steps and was unable to perform simple calculations. His speech was fluent, but he often used similar-sounding word substitutions. He could immediately recall three out of three words but recalled none of them after 5 minutes. Examination of the cranial nerves revealed clinically significant paratonic rigidity. Myoclonic jerks were seen in the arms, with symmetrically brisk reflexes. The reflexes in

Clinical trial eligibility criteria: eligible ages (years): 40.0-999.0,  Alzheimer's Disease Dementia AD group  Male or female patient, aged ≥ 40 years old included at entry Patients having a clinical diagnosis of probable AD according to DSM-IV TR [F00.xx] and National Institute of Neurological and Communicative Disorders and Stroke/Alzheimer's Disease and Related Disorders Association (NINCDS-ADRDA) criteria Written informed consent obtained from the patient or, if appropriate, from legal representative according to local laws and regulations Evidence that brain imaging (either cerebral CT-scan or cerebral MRI) was performed to settle the AD diagnosis, and that the results are compatible with AD diagnosis Neurological exam without any particularities or without any specific focal signs likely to be related to other conditions than AD Patient compliant with study procedures Non AD demented group  Male or female patient, aged ≥ 40 years old included at entry Patients having a clinical diagnosis of dementia which can be one of the following   AD group  Any pathology, medical condition or symptoms that may lead to reconsider the initial diagnosis of probable AD, or that may rend the initial diagnosis of probable AD doubtful at entry, according to the opinion of the investigator Current or recent history of drug or alcohol abuse or dependence Diagnostic of Mild Cognitive Impairment defined by subjective complaints from the patient regarding memory and/or cognitive symptoms, objective memory and/or cognitive impairment at testing but not meeting AD diagnostic and not affecting daily living activities Current diagnosis of brain tumour Any current pathology or medical condition, for which blood sampling may involve a risk for the patient's health, according to the opinion of the investigator Pregnancy Patient who is not registered at "Sécurité Sociale" Current participation in another study using an investigational non-marketed product Non-AD demented group