Who is affected?
On the basis of comparisons of large groups of people with Alzheimer's disease with others who have not been affected, researchers suggest that there are a number of risk factors. This means that some people are more likely to suffer from the disease than others. However, it is unlikely that the disease could be traced to a single cause. It is more likely that a combination of factors lead to its development, with the importance of particular factors differing from one person to another.
About one person out of twenty over the age of 65 develops Alzheimer's disease and less than one person in a thousand under the age of 65. However, it is important to note that although people do tend to become forgetful as times goes on, the vast majority of people over 80 stay mentally alert. This means that although the likelihood of developing Alzheimer's disease increases with age, old age does not itself cause the disease. Nevertheless, recent evidence suggests that age related problems such as arteriosclerosis may be important contributing factors. Also, as people are now living longer than in the past, the number of people with Alzheimer's disease and other forms of dementia will most probably increase.
Some studies have suggested that more women are affected by the disease than men at any one time. However, this can be misleading because women as a group live longer than men. This means that if men were to live as long as women and did not die of other illnesses, the number with Alzheimer's disease would be about the same as that for women.
Genetic factors (Heredity)
In an extremely limited number of families Alzheimer's disease is a dominant genetic disorder. Members of such families inherit from one of their parents the part of the DNA (the genetic make-up), which causes the disease. On average, half the children of an affected parent will develop the disease. For the members of such families who develop Alzheimer's disease, the age of onset tends to be relatively low, usually between 35 and 60. The onset is fairly constant within the family. A link between chromosome 21 and Alzheimer's disease has been discovered. As Down's syndrome is caused by an anomaly in this chromosome, many children with Down's syndrome will develop Alzheimer's disease if they reach middle age, although they may not display the full range of symptoms.
There is evidence to suggest that a person who has received a severe blow to the head may be at risk of developing Alzheimer's disease. This risk is higher if at the time of the injury the person is over 50, has a specific gene (apoE4) and lost consciousness just after the accident.
There is no conclusive evidence to suggest that any particular group of people is more or less likely to develop Alzheimer's disease. Race, profession, geographical and socio-economic situation are not determinants of the disease. However, there is mounting evidence to suggest that people with a higher level of education are at less risk than those with a lower level of education.
Last Updated: Wednesday 26 August 2015