With nearly 860 000 people suffering from Alzheimer type dementia in France, this disease is now a central focus. It is characterised by slow neuron degeneration beginning at the level of a specific area and then extending to the rest of the brain.
Alzheimer's disease is the most common neurodegenerative disease affecting the elderly. The increase in the average lifespan due to improved living conditions is one of the reasons for the rise in the number of people affected by this disease. Today, it is estimated that 900,000 people suffer from Alzheimer's-type dementia in France, and 35 million worldwide. While the onset of dementia before the age of 65 is rare (0.5%), the incidence rises to between 2% and 4% after that age. It then increases proportionately with age, reaching over 15% by the age of 80. The disease is increasingly affecting women (1 in 4 women and 1 in 5 men over the age of 85).
Causes and biological mechanisms of Alzheimer's disease
Hereditary or ‘familial’ forms of Alzheimer's disease are very rare, accounting for less than 1% of cases. They appear before the age of 60. Symptoms sometimes begin in the thirties or forties. The disease is not hereditary in the strict sense of the term in 99% of cases, but genetic predisposing factors have been identified, i.e. factors that increase the risk of developing the disease. For example, carrying a specific allele of the ApoE gene (ApoE4), which is involved in several neuronal protection mechanisms, increases the risk of developing the disease (3 to 15 times depending on whether you carry one or two APOE4 alleles). However, this allele is neither sufficient nor necessary for developing the disease, since some people who carry it will not develop the disease, whereas non-carriers will.
Certain so-called 'environmental' factors have been associated with Alzheimer's disease, such as chronic sleep deprivation or the use of certain psychotropic drugs, such as benzodiazepines, which can increase the risk of developing the disease. Recently, a list of risk factors for Alzheimer's disease was published, although it is still incomplete. These include excessive alcohol consumption, head injuries, air pollution, low levels of education, high blood pressure, hearing problems, smoking, obesity, depression, physical inactivity, diabetes and social isolation.
The degeneration of neurons that occurs in Alzheimer's disease is the result of the concomitant progression of two types of lesion: firstly, the abnormal accumulation on the outside of cells of ß-amyloid peptides (also known as A-beta peptides or Aß peptides), leading to the formation of ‘amyloid plaques’, also known as ‘senile plaques’, and secondly, the abnormal accumulation of the TAU protein in neurons, leading to their degeneration.
Symptoms and diagnosis of Alzheimer's disease
Memory loss is often the first symptom of Alzheimer's disease, which helps to guide the diagnosis. This is followed by problems with executive functions and temporo-spatial orientation, followed gradually by problems with language (aphasia), writing (dysorthographia), movement (apraxia), behaviour and mood (anxiety, depression, irritability). The fact that the patient is unaware of his or her deficits (anosognosia), but that it is relatives who report the disorders, is in itself a diagnostic criterion.
Diagnosis is clinical, and now involves the use of high-performance diagnostic tests such as a full neuropsychological assessment of cognitive functions, imaging tests such as MRI and glucose PET scans, which highlight the areas of the brain that are suffering, and finally lumbar puncture, which is capable of showing the biological signs of the disease, i.e. the presence of abnormal deposits of amyloid and tau protein.
Treatments for Alzheimer's disease
The aim of Alzheimer's treatment today is to slow the progression of the disease and enable patients and their families to adapt to the handicaps they face. Treatment is therefore multidisciplinary.
Unfortunately, there is still no treatment that directly addresses the causes and mechanisms behind the disease. Two types of medication (acetylcholinesterase inhibitors and memantine) have been validated and are used worldwide. They strengthen brain circuits and, in some cases, stabilise the clinical picture of the disease.
