Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia. First described by Alois Alzheimer in 1906, this disease is characterized by a progessive and irreversible destruction of nervous cells (neurones) located in two distinct brain region : hippocampus and  polymodal associations areas.

The degenerating process and the resulting neuronal loss lead first to memory impairment, then to language, personality and behavour disorders and later to total loss of autonomy anddementia. At the end of the disease, most, if not all the cortical brain areas, as well as many subcortical nuclei, are heavily filled with two different types of lesions: amyloid plaques and neurofibrillary

In degenerating neurons, the microtubule network is transformed into abnormal filaments made up of pathological Tau proteins. During this period, amyloid plaques are forming from aggregation of an extracellular peptide called Amyloid beta (Abeta). This poorly soluble peptide isrealesed from Amyloid precursor protein degradation. 

Since Alzheimer's observations, researchers have cumulated a better understanding of pathologic changes in brain and cognitive impairments characterics associated with the disease. Several genes associated to familial cases were identified. However these cases represent less than 2% of patients. Despite heavy R&D efforts, exact causes and the mechanism still remain uncertain. 

Alzheimer's disease is the 4th leading cause of death in aldults and affects egally men and women. Most people diagnosed with AD are older than age 65; however, AD can occur in people in their 40s and 50s.

Diagnostic methods

There is currently no simple method to ensure  the AD diagnostic. The final diagnostic is obtained only after death with an autopsy to identify amyloid plaques and neurofibrillary tangles in brain areas dedicated to memory, learning and intellectual functions.

However, identification of probable alzheimer's disease can be obtained with cognitive tests. These tests are unfortunately quite biased.

The diagnostic can be refined with neuroimagery (PET-scan ou MRI) to identify atrophy in specific brain areas.

Biological exams are also available to refine the diagnostic. However, the method uses identification of biological markers in cerebrospinal fluid. A lumbar puncture is necessary to  obtain this biological fluid and is thus more aggressive.

Blood tests were recently annouced and should soon be available on the market.