March 11, 2004
Some people inherit a gene that makes them more susceptible to the most common form of Alzheimer'sthe late-onset form of the disease that appears in old age. The gene, called APOEe4, has long been thought to influence whether you will develop the mind-robbing ailment. But, a new study indicates, that APOEe4 more strongly influences when a person will develop Alzheimer's rather than if, they will.
The study looked at more than 3,300 seniors living in Cache County, Utah, a community that boasts one of the largest concentrations of long-lived seniors in the United States. Few of the elderly there smoke or drink, and many live to 90 and beyond.
The researchers found that people who inherited a single copy of the APOE e4 gene were more likely to develop symptoms of Alzheimer's in their sixties or seventies, rather than in their eighties or nineties. Inheriting two copies of the gene made it even more likely that symptoms would appear at an earlier age.
Although carrying the APOE e4 gene raises your risk of Alzheimer's at an earlier age, it by no means assures you will get the disease. The study found that even among those who live to be 100, 28 percent of these elderly men and women do not develop severe memory problems. Even some of those who carried one or two copies of the APOE e4 gene did not develop symptoms of Alzheimer's.
Old Age and Alzheimer's
It has long been known that the older you get, the more likely you are to develop symptoms of Alzheimer's disease. Studies show that among seniors, the incidence of Alzheimer's double every five years. At age 85 and beyond, about 45 percent of seniors exhibit the kinds of severe memory problems that indicate Alzheimer's disease.
Certain genes are known to cause an inherited form of Alzheimer's. Among these are the presenilin genes, which result in Alzheimer's at an early agein some cases as early as your thirties or forties. These genes are rare, however, and old age remains a primary risk factor for the development of Alzheimer's.
Alzheimer's, though, is by no means an inevitable consequence of aging. In addition to genetics, many other factors likely influence whether or not you will develop memory problems in old age. What you eat, how much you exercise, formal education, smoking, and other factors have all been implicated.
For more on the APOE gene, risk factors for Alzheimer's disease, and the search for a cure, visit www.ALZinfo.org.
The findings referred to here were published in the May issue of the Archives of General Psychiatry, a journal published by the American Medical Association.
Ara S. Khachaturian, et al: "Apolipoprotein E e4 Count Affects Age at Onset of Alzheimer Disease, but Not Lifetime Susceptibility: The Cache County Study." Archives Gen Psychiatry 2004;61:518-524.