Date: May 1st, 2001
The role of genetics in determining the quality and length of human life is a million-dollar question right now. Scientists are discovering bits and pieces of the puzzle, but they're still scratching their heads about how it all fits together. What exactly do we know about our genes and how we age? Is health and longevity determined more by genes or lifestyle choices?
Caleb Finch, Ph.D., professor of Gerontology and Neurobiology at the University of Southern California, has been studying brain aging with colleagues in his lab. (When he's not in his lab, Dr. Finch, or "Tuck" as he's known to friends, can be found touring, playing and recording with his old time, southern mountain-style band, aptly called the Iron Mountain String Band.)
We asked him to tell us how close scientists are to finding answers to the age-old question: how can I live a longer, healthier life?
Q: What do we know now about the relationship between our genetic makeup and the diseases of aging?
A: We know that there are families with a rare genetic history of early-onset Alzheimer's, diabetes, cancer and heart disease — families whose carriers of these strong genes die before 50. Some of these diseases show up later in the general population as well, and when they show up later, we don't know if there is a strong genetic effect. There also are people who have two copies of a "bad" gene who live into their 80s, 90s and more without ever getting the disease. So we don't know if the absence of disease is due to lifestyle or the effect of some other gene or genes. There are many complicated questions that must be answered before we really understand the relationship between genetics and disease.
Q: How is longevity related to genes, and how much can be attributed to environmental and lifestyle factors?
A: If you look at longevity itself, and not disease, you find that identical twins, by the time they're 80, have no closer life spans than other members of the general community in which they live. So you might draw the conclusion that after a certain age, genes have a relatively weak affect on life span. On the other hand, there are families whose members seem to have an unusually long life span despite environmental factors. Overall, about one-third of life span within a species can be associated with particular gene differences between individuals. We don't know what the other two-thirds is yet. Is it the environment interacting with genes? We just can't tell yet.
Q: What is the Human Genome Project likely to reveal in the next 5-10 years?
A: In the next 5-10 years, the Human Genome Project will make a huge amount of progress in identifying a "telephone book" — an inventory of each individual's genes and how they differ from others in their family. But it's going to be a very long time before we work out all of the details for individuals — what their risk factors are for disease and how we can optimize their environment for their particular set of genes.
Q: How useful is genetic testing at this point?
A: It's useful to know if you're carrying a rare gene risk factor, but in many cases there is not much you can do about it. And it confronts people with very difficult issues and choices. For example, some women are choosing to have their breasts removed because their mothers and grandmothers had breast cancer. That's a very difficult choice, although at least there is a choice.
Visit our Genetics in Aging web feature to keep up-to-date on the latest findings on genetics and aging. Bridging the education gap for people who are concerned about their chances for healthy aging and the possible links of inherited disease, Genetics in Aging shows how your genetic heritage and lifestyle habits relate to your personal health risks. Understanding the interplay between your body's genetic 'roadmap' and life choices can improve your odds of leading a more vital, productive and independent life.