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Alzheimer's disease

Common manifestation of dementia, thought to afflict 1 in 20 people over 65. After heart disease, cancer, and strokes it is the most common cause of death in the Western world. Attacking the brain's ‘grey matter’, it is a disease of mental processes rather than physical function, characterized by memory loss and progressive intellectual impairment. It was first described by Alois Alzheimer in 1906. Dementia affects nearly 18 million people worldwide, 66% of whom live in developed countries; this includes some 4 million people in the USA, and over 750,000 in Britain (2001). Numbers are expected to rise with the world's ageing population, reaching an estimated 34 million worldwide by 2025.

Causes

Various factors have been implicated in causing Alzheimer's disease including high levels of aluminium in drinking water and the presence in the brain of an abnormal protein, known as beta-amyloid.

In 1993 the gene coding for apolipoprotein (APOE) was implicated. US researchers established that people who carry a particular version of this gene (APOE-E4) are at greatly increased risk of developing the disease. It is estimated that one person in thirty carries this protein mutation; in the USA the figure is as high as 15%. The suspect gene can be detected with a test, so it is technically possible to identify those most at risk. As no cure is available such testing is unlikely to be widespread.

A second Alzheimer's gene was identified in 1997. The gene, HLA-A2, increases the speed at which the disease begins. The Neurology report stated that if a person has both HLA-A2 and APOE-E4, he or she may reach dementia a decade earlier than those with only one of the genes.

In December 1999, after successful animal trials, a US trial was approved to ascertain whether gene therapy can be used to slow the development of Alzheimer's disease.

In 1999 researchers in Boston, Massachusetts, discovered an enzyme, presenilin, that produces protein plaques associated with the disease. Presenilin opens up the amyloid parent protein (APP) that then releases beta-amyloid, or A-beta.

Diagnosis

US researchers began trialling a simple eye test in 1994 that could be used to diagnose sufferers. The drug tropicamide causes marked pupil dilation in those with the disease, and only slight dilation in healthy individuals.

Treatment

Some researchers are convinced that, whatever its cause, Alzheimer's disease is essentially an inflammatory condition, similar to rheumatoid arthritis. Although there is no cure, trials of anti-inflammatory drugs have shown promising results. Also under development are drugs which block the toxic effects of beta-amyloid. A 1996 study by US neuroscientists found that oestrogen skin patches were also beneficial in the treatment of female Alzheimer's patients, improving concentration and memory.

According to a report released in June 2001 by the Center for Disease Control and Prevention, Alzheimer's disease was the 8th main cause of death in the USA in 1999, rising from 12th position in 1998. The report found that the rise resulted from a new method of determining cause of death: deaths from Alzheimer's have previously often been ascribed to other causes, such as pneumonia. It also estimated that around 4 million US citizens have Alzheimer's, and predicted that this figure would increase to 14 million by 2050.

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