Amyloid Alzheimer's

Amyloid is produced when a much larger protein, the amyloid precursor protein, is broken down. Amyloid then accumulates as plaques (deposits) on the outside of nerve cells. 

Amyloid deposits are believed to be toxic causing damage to nerve cells many years before the onset of dementia. There is now evidence that amyloid abnormalities appear at an early stage of Alzheimer’s disease, in both cognitively normal people and those suffering mild cognitive impairment before they go on to develop Alzheimer’s dementia²⁷.

Identifying amyloid deposits in a person requires either a brain biopsy or PET (positron emission tomography) imaging. Amyloid imaging provides complementary information about amyloid that cannot be gathered even by very detailed clinical examination²⁸.

The presence of amyloid can rule out some other types of dementia (such as frontotemporal dementia) that are not associated with amyloid deposition²⁹.

We are still learning about amyloid and its exact role in prodromal Alzheimer’s disease.

Being able to identify amyloid in a person’s brain when they are in the prodromal stage of Alzheimer’s disease may offer a new treatment approach that could potentially prevent or delay Alzheimer’s disease. Once a patient has established Alzheimer’s, it is likely to be too late to reduce the amyloid deposits.

Facts about Tau

The second hallmark of Alzheimer's disease is tangles in a protein called tau.

Tau protein is produced by normal healthy nerve cells, however during Alzheimer’s disease an abnormal version is produced that doesn’t function correctly. This version, known as p-tau, causes tangles within the cells and effectively strangles the neurons (nerve cells), which then die.

In one study, decline in memory measured in people with mild cognitive impairment correlated with tangles of tau protein occurring – about 12 years before clinically defined Alzheimer’s disease²⁰.

As a result of neurodegeneration, shrinking (atrophy) of the hippocampus occurs in Alzheimer’s. The hippocampus is a region of the brain that is essential for memory.

Brain atrophy is a structural change in the brain that can be detected by MRI scans.

Atrophy can happen in healthy brains as they age, and is caused by brain cell loss. However, this atrophy is more noticeable in people with dementia and has a certain pattern depending on which form of dementia is present³⁰.

There is now also evidence that greater atrophy of a certain region of the hippocampus may predict which patients with mild cognitive impairment will progress to Alzheimer’s disease³¹.

How is prodromal Alzheimer’s assessed?

Diagnosing prodromal Alzheimer’s disease can be difficult, and the doctor may refer you to a specialist consultant.

Assessments are varied, but may include the following – some of these can only be done by a specialist²¹:

• A physical examination
• Memory tests
• Brain scans such as CT/MRI and PET scans
• Biomarkers

Memory test assessments

There are a range of memory tests that healthcare professionals use to help diagnose the early stages of Alzheimer’s disease. The Mini Mental State Examination (MMSE) is one of the most commonly used tests for complaints of memory problems or when a diagnosis of dementia is being considered³².

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