The benefits of early detection

Characteristic disorders of Alzheimer's disease do not appear abruptly. On the contrary, they are the result of a relatively slow process whose early stages may go unnoticed. Research is now working on the development of effective screening tests even before the onset of symptoms. Such discoveries will make it possible to implement preventive strategies.

Medical imaging as a predictive tool

Too often, the first symptoms of Alzheimer's disease are not identified, the relatives and the patient himself tending to put memory problems on the account of age. The family doctor is the first to be able to detect these symptoms. Today, tests and questionnaires can enable him to identify the disease as "probable", to specialists (neurologist, psycho-neurologist, geriatrician) to confirm the diagnosis.

Demonstration of tau and amyloid beta proteins

When a patient is diagnosed early, treatment can be given to certain forms of rehabilitation, which delay the onset of the disease. Schematically, the sooner the disease is detected, the sooner the patient can be followed and the more the development of the disease will be delayed.

Many studies have shown a higher risk of being reached if a parent is already affected. Thus, one would have thought that the development of genetic screening tests seemed logical. However, the heredity of the most common form of the disease (the sporadic form which represents more than 90% of the cases) is still uncertain today. Moreover, regardless of the genes identified, people will not necessarily develop the disease. At the very most, we can identify "genetic risk factors". If the solution is not in our genes, what are the other paths of research? Three recent findings provide interesting answers.

In July 2001, Nick Fox 1 stated that he had developed a new brain-scanning technique capable of screening Alzheimer's patients before the onset of symptoms. The brains of 44 people were examined by a magnetic resonance imaging (MRI) system. MRI makes it possible to make "photographs" in sections of the brain. All these images are then collected and the area studied is rendered in three dimensions.

Compressed and processed by an adapted computer system, these data demonstrated low alterations in brain tissue. In four individuals with early familial Alzheimer's disease, this progressive atrophy affected some areas of the brain, especially in the medial temporal lobe and parietal lobe, three years before the onset of the first disorders. During the study, which continued over 5 to 8 years, these subjects developed the disease.

In April 2001, another study 2 highlighted the value of MRI in distinguishing Alzheimer's disease from other types of dementia. Semantic dementia, for example, characterized by impaired comprehension of words is very close to Alzheimer's disease.

But the MRI of 30 subjects (10 with Alzheimer's disease, 10 with semantic dementia and 10 with normal cognitive functions) highlighted differences. For semantic dementias, cerebral tissue involvement is confined to the left hemisphere and in particular the frontal area. For Alzheimer's disease, no area of ​​the brain appears to be the preferred target of this atrophy after the disease is triggered.

More recently, Dr. Mony de Leon 3 of the New York Medical Center was able to identify signs of Alzheimer's disease several years before the onset of the first symptoms.

The researchers performed a tomographic scan of positron emissions on 48 people aged 60 to 80 years. Schematically, this imaging technique provides an "instant snapshot" of cerebral functioning.

Twelve patients had reduced activity in certain areas of the brain. Three years later, 11 patients developed memory impairment and one was diagnosed with Alzheimer's.

"Today, Alzheimer's disease can be thought of as a two-shot rifle: it results from the dysfunction of two proteins, APP (Amyloid protein precursor) and tau protein (naturally induced dysfunction due to age and Encountered in all people over 70 years of age.) It is the meeting of these two dysfunctions that leads to pathology, "declared Mr. Delacourte, research director at the INSERM on Cerebral Aging and Neuron Degeneration.

Based on these recent advances, researchers at the University of Texas wanted to evaluate the concentration of these two proteins in the cerebrospinal fluid. Theoretically

RESULTS: Of the 241 people with signs of mental decline, the researchers successfully screened 94% of patients diagnosed as "probable" Alzheimer's patients.

Based on advances in medical imaging or cerebrospinal fluid analysis, screening tests may soon improve the diagnosis of the disease. Identifying it before the onset of the first symptoms would make it possible to initiate treatment at early stages and thus to delay the first disorders. At a time when the development of a curative vaccine is becoming more and more feasible, such tests would designate patients to be vaccinated as a priority. Finally, these discoveries will allow us to better understand the mechanisms of progression of the disease and to test the effectiveness of treatments in the very early stages.

1 - Lancet 2001 Jul 21,358 (9277): 201-205; 2 - Annals of Neurology Volume 49, Issue 4, 2001. Pages: 433-442; 3 - Proc Natl Acad Sci USA 2001 Sep 11,98 (19): 10966 -10971; 4 - Arch Neurol. 2001 Mar, 58 (3): 354-6.

Magnetic Resonance Imaging

Amyloid beta are responsible for the formation of senile plaques, which accumulate in the brain of the sick. Sticking together to form these clusters, their concentration in the cerebrospinal fluid should be low, but the accumulation of tau proteins that disturb the brain, so their concentration should appear high. Code>