What is Alzheimer's disease?

Sep 30, 2019

Alzheimer’s disease, which is the most common form of dementia, is an incurable degenerative disease. Neurons in certain parts of the brain are destroyed which leads to deficits in cognitive functions, such as memory, language skills, and behavior. Clinical diagnosis can be supported by biomarkers that detect the presence or absence of the disease. This will become even more important in the future, when new treatments of Alzheimer’s disease will become available.
 

About Alzheimer's disease

Dementia affects 5-8% of all people above 60 years of age, increasing to around 40% of people older than 90 years.1

Alzheimer’s disease, which is the most common form of dementia, is an incurable degenerative disease. Neurons in certain parts of the brain are destroyed which leads to deficits in cognitive functions, such as memory, language skills, and behavior.

Typical Alzheimer lesions start to develop in the brain already 10 to 20 years before the first symptoms (the pre-symptomatic phase of the disease). Only when the neuronal injury evolves and the cognitive reserve decreases, symptoms start to manifest.

In the early stages the disease only provokes minor symptoms such as mild mental confusion, difficulties finding the right words, and remembering recent events.

As the disease progresses it leads to a total loss of the patient’s autonomy: incapacity to remember and recognize people, objects, places etc.

The destruction of neurons in the brain is caused by an abnormal accumulation of different types of proteins: the amyloid peptide and the hyperphosphorylated Tau (Tubule-Associated Unit) proteins.

It is still unknown today what causes abnormal accumulation of these proteins in the brain.
 

Diagnosing Alzheimer's disease

Alzheimer’s disease is primarily diagnosed through clinical neurological examination, a cognitive assessment, and a structural and/or functional brain imaging in order to identify cerebral atrophy and hypometabolism in regions of the brain that are typically affected by Alzheimer’s disease.

This primary diagnosis can be further supported by using either amyloid brain imaging or fluid biomarkers, both of which are recent techniques that can help identify the biomarkers representing underlying changes in the patient’s brain due to Alzheimer’s disease.

Amyloid brain imaging consists of injecting radioactive tracers in the blood of the patient (“in vivo”) that allows visualization of the amyloid plaques in the brain.

Amyloid brain imaging is reserved for centers equipped with specific facilities and expensive instruments, which explains the high cost associated with a brain scan.  

Diagnosis based on fluid biomarkers (also known as “in vitro” diagnostics), requires the collection of a sample of the cerebrospinal fluid (CSF) that surrounds the brain and extends into the spinal canal of the patient.

The analysis of this sample allows the detection of four proteins; two forms of amyloid (Aβ1-42 and Aβ1-40) proteins and two forms of Tau (Total Tau and phospho-Tau) proteins. 

If the patient has Alzheimer’s disease, then these proteins will be present in abnormally low (Aβ1-42 and Aβ1-42/Aβ1-40 ratio) and high (Total Tau and phospho-Tau) levels. The Aβ1-42 protein levels will even be low before the symptoms of the disease start to show.

The CSF sample collection is a fast procedure and far less expensive than amyloid brain imaging. The patient is able to go to a center close to his/her home where the sample is taken by a medical doctor.

The sample is then sent to a clinical laboratory for analysis. In the laboratory multiple tests can be done on the same patient sample. This allows the doctor to gather a lot of additional information – a complete biochemical profile - for a far better characterization of the dementia.

In the future, when new treatments of Alzheimer’s disease will become available, this technique can be offered to at-risk populations in order to detect the presence or absence of the disease, even at an early stage. And hence give each patient a chance to receive better care and preserve a high quality of life.

References:

  1. World Alzheimer Report 2015
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