What causes Alzheimer’s disease?

While the exact cause of Alzheimer’s disease is unclear, researchers have found that genetic, lifestyle and environmental risks may contribute to  its development.

On a physiological level, what we do know is that that as the disease develops, protein structures referred to as ‘plaques’ and ‘tangles’ build up in the brain. These abnormal structures cause the nerve cells (neurons) to lose connection to one another, hampering the transmission of signals around the brain. This eventually leads to the death of nerve cells  resulting in brain damage and brain tissue loss which results in brain shrinkage.

The two types of abnormalities responsible for cell destruction in Alzheimer’s are explained below:

• Plaques, called amyloid plaques, are groups of protein that disrupt the communication between the nerve cells (neurons) of the brain. This disruption leads to damage and the eventual death of the nerve cells.
• Neurofibrillary tangles are abnormal threads of tau proteins that have collected in the brain cells of someone with Alzheimer’s. Tau proteins help to make up the structure of a microtubule within nerve cells, which transports various nutrients and chemicals from one part of the cell to another. In Alzheimer’s the abnormal tau proteins cause the microtubules to collapse, preventing these essential nutrients and chemicals from being carried throughout the brain.

The role of genetics and epigenetics in Alzheimer's disease

Genetics is also known to play a profound role in the development of Alzheimer’s disease. The apolipoprotein E gene (APOE), is known for playing a part in the late-onset of the disease. However, it is important to remember that even if one has this gene, it does not mean that the development of Alzheimer’s is certain, it is merely a factor that may increase the risk of its development.

Another potential cause of Alzheimer's has been linked to changes in certain genes, for example, people with Down Syndrome have an increased risk of developing Alzheimer’s in later life, which is thought to be the result of their extra copy of chromosome 21.

While genetics are an important factor in Alzheimer's development, they are not soley responsible for its progression.

Health, environmental and lifestyle causes

Factors such as health, environment and lifestyle are all thought to play a role in the development of Alzheimer’s disease. These are discussed in greater deal under the risk factors section of this article.