Alzheimer's disease: Causes and prevention

What is Alzheimer's disease?

Alzheimer's disease or Alzheimer's-type dementia is a progressive degeneration of brain tissue that primarily affects people over the age of 65. It is the most common cause of dementia and is marked by a devastating mental decline. Intellectual functions such as memory, comprehension, and speech deteriorate.

Attention tends to stray, simple calculations become impossible and ordinary daily activities become increasingly difficult, with growing bewilderment and frustration. These symptoms tend to worsen at night. Dramatic mood swings occur - outbursts of anger, bouts of fearfulness, and periods of deep apathy. The sufferer, increasingly disoriented, may wander off and become lost. Physical problems, such as an odd gait or a loss of coordination, gradually develop. Eventually, the patient may become physically helpless, incontinent, and unable to communicate.

Alzheimer's disease can run its course from insidious onset to death in just a few years, or it may play out over a period of time as long as 20 years. More often, however, people suffer with Alzheimer's disease for about nine years. In the UK, the Alzheimer’s Society estimates that one person out of 14 aged 65 and over has the disease. People over the age of 80 are thought to have a one in six chance of developing the condition. The Alzheimer’s Society believes the disease is the direct cause of 15% of all deaths in England each year. Women are more susceptible than men and more than half of all nursing home residents suffer from Alzheimer's or another form of dementia.

What causes Alzheimer's disease?

People are more likely to develop Alzheimer's disease as they grow older, but the disease is not a natural result of ageing. It is an abnormal condition the causes of which continue to be investigated.

The gradual loss of brain function that characterises Alzheimer's disease seems to be due to two main forms of nerve damage:

• Nerve cells develop tangles (neurofibrillary tangles)
• Protein deposits known as plaques build up in the brain.

Researchers are not yet sure why or how these processes occur, but some of the most promising recent research points to a normally occurring blood protein called ApoE (for apolipoprotein E), which is required for the transport of fatty substances in the body.

As with all proteins, the form of ApoE that each person has in their body is genetically determined and several different types have been identified - some of them apparently associated with a higher risk of Alzheimer's. It may be that certain forms of ApoE lead to the nerve damage.

Another possibility is that the protein, perhaps working in combination with other substances, is involved in the formation of the plaques. Whether or not ApoE partly causes Alzheimer's disease, genes almost certainly play a role in the disease and a person with a parent who had Alzheimer's disease is at higher risk.