Memory disorders are the main problem caused by the disease. The patients begin by forgetting recent events, but conserve memories of the distant past. The disease evolves inexorably, with a worsening of the intellectual deficits (disorders of memory, recognition, language, reasoning, …) and the appearance of behavioural disorders, all of which lead to a loss of autonomy and therefore dependency.
These cognitive disorders result from the loss of nerve cells in the superficial regions of the brain (the cerebral cortex), specifically in structures that play a role in the control of memory (hippocampus), language (temporal cortex), visual perception (occipital cortex), etc. It's the prototype of a neurodegenerative disease characterized by a slow loss of nerve cells that is nevertheless more rapid than in normal aging and affects only some, not all, brain regions. The nerve cells begin by "suffering" – they are "sick" – then, beyond a certain threshold, they disappear.
Alzheimer's disease has several different clinical presentations and several different causes. Some of the causes, as in hereditary cases, are well known; others remain a mystery, as in the vast majority of sporadic cases of the disease. The mechanisms underlying the suffering and death of the vulnerable neurons remains unknown in most cases, but an abnormal accumulation of a protein known as beta-amyloid probably plays an essential role. Most high level research is now focused on the search for factors that confer a genetic predisposition to the disease and the identification of the biochemical interactions (particularly those involving beta-amyloid) leading to neuronal death, which suggest molecular targets for drugs that can interrupt the fatal sequence of events. At present, there is no treatment for Alzheimer’s disease …
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