"Alzheimer's disease" is the term used to describe a dementing disorder marked by certain brain changes, regardless of the age of onset. Alzheimer's disease is not a normal part of aging--it is not something that inevitably happens in later life. Rather, it is one of the dementing disorders, a group of brain diseases that lead to the loss of mental and physical functions. The disorder, whose cause is unknown, affects a small but significant percentage of older Americans. A very small minority of Alzheimer's patients are under 50 years of age. Most are over 65.

Alzheimer's disease is the exception, rather than the rule, in old age. Only 5 to 6 percent of older people are afflicted by Alzheimer's disease or a related dementia--but this means approximately 3 to 4 million Americans have one of these debilitating disorders. Research indicates that 1 percent of the population aged 65-74 has severe dementia, increasing to 7 percent of those aged 75-84 and to 25 percent of those 85 or older. At least half the people in U.S. nursing homes have Alzheimer's disease or a related disorder; in 1985, the annual cost of caring for individuals with Alzheimer's disease and related dementias in institutional and community settings was estimated between $24 billion and $48 billion for direct costs alone and is probably higher today. As our population ages and the number of Alzheimer's patients increases, costs of care will rise as well.

Although Alzheimer's disease is not curable or reversible, there are ways to alleviate symptoms and suffering and to assist families. Not every person with this illness must necessarily move to a nursing home. Many thousands of patients--especially those in the early stages of the disease--are cared for by their families in the community. Indeed, one of the most important aspects of medical management is family education and family support services. When, or whether, to transfer a patient to a nursing home is a decision to be carefully considered by the family.

The main risk factor for Alzheimer's disease is increased age. The rates of the disease increase markedly with advancing age, with 25 percent of people over 85 suffering from Alzheimer's or other severe dementia.

Some investigators, describing a family pattern of Alzheimer's disease, suggest that in some cases heredity may influence its development. A genetic basis has been identified through the discovery of several genetic markers on chromosomes 21 and 14 for a small subgroup of families in which the disease has frequently occurred at relatively early ages (beginning before age 50). Some evidence points to chromosome 19 as implicated in certain other families that have frequently had the disease develop at later ages.

At the same time, data indicate that the likelihood that a close relative (sibling, child, or parent) of an afflicted individual will develop Alzheimer's disease is low. In most cases, such an individual's risk is only slightly higher than that of someone in the general population, where the lifetime risk is below 1 percent. And, of course, many disorders have a genetic potential that is never expressed--that is, despite being at risk for a certain illness, one might go through life without ever developing any symptom of the disease.