At age 23, Katharine Moser took the genetic test for the Huntington's disease (HD). The news was not good. She has the version of the HD gene that will eventually rob her of her ability to walk, talk, swallow and think. The gene that will cause Moser's illness was inherited from grandfather through her mother. Everyone carries the gene, but only those who have a segment that repeats three bases of genetic code cytosine, adenine and guanine (CAG) many times will get it. People with fewer than 35 GAG repeats will not suffer the disease; however, people with more repeats will inevitably succumb to it. The more repeats, the sooner the onset of the disease. In Moser's case, her HD gene has 47 CAG repeats which means that she is likely to begin experiencing symptoms by the time she reaches her mid-30s. In many ways, Moser is blazing a trail for the rest of us. Improved genetic testing will tell more and more of us about our future health and likely ends.
Hold on a minute. Don't we already know a lot about our future health and how our lives are likely to end without all that fancy new genetic technology? We all know that we're going to die. More than half of us will die of heart disease or cancer. Using actuarial tables we can figure out your chances of making it to any specified age. For example, actuarially there is a 50 percent chance that I will live just another 25 years. Damn! On the other hand, longevity researcher Thomas Perls at Harvard offers a longevity calculator that takes into account lifestyle, family history and so forth. My score, including my less-than-exemplary drinking, exercise and red meat habits: a 50 percent chance of making it another 31 years. Life insurance companies already make pretty good guesses how long you're likely to live based on family medical history and lifestyle habits, so who needs genetic testing?
The problem is that life expectancy calculations are an average. The Wharton Life Expectancy calculator gives me a 50 percent chance of living an additional 31 years too. However, there is a 25 percent chance that I will die in 23 years. On the other hand, there is a 25 percent chance that I might have as long as 41 more years. The difference of 18 years matters.
Future tests, including genetic tests, could narrow the range of your specific life expectancy. In addition, such tests will be able to tell what your greatest risks are. Right now, tests look for disease risks based on specific genetic flaws. For example, altered BRCA1 and BRCA2 genes boost the chance that a woman will have breast cancer by 3 to 7 times. People with the APOE4 variant of a gene involved with cholesterol transport are at increased risk of Alzheimer's disease (AD). Unlike the HD gene, having the APOE4 variant is not a guarantee of future illness. The environment also plays a big role. One study suggests that drinking alcohol increases the risk of AD for carriers of the APOE4 allele. Recent research indicates that the herpes virus that causes cold sores may also interact with the APOE4 allele to increase the risk of AD.
In addition to environmental influences there are gene interactions that affect a person's risk of AD. For example, some research hints that carriers of both the APOE4 and a version of the CYP46 gene have a 10 times greater than average risk of AD. (Other research casts some doubt on this conclusion.) Nevertheless, researchers are developing data banks that compile possible associations between various genes and the risks of disease. Genetic researchers are already investigating which sets of genes, called haplotypes, combine to increase a person's risk of various diseases including cardiovascular disease. One can imagine in the not too distant future, say ten years, when a comprehensive panel of genetic tests will identify a variety of disease causing and health promoting haplotypes. You may test "positive" for haplotypes that increase risk for kidney cancer and deep vein thrombosis and for others which reduce your risk of Alzheimer's disease and diabetes. Analyzing such genetic information may put narrower limits on your life expectancy.
Of course, the new tests will also give you options for stalling the arrival of the Grim Reaper. For example, if it turned out that you carry two copies of the APOE4 allele, you may choose to cut back on your drinking in order postpone dementia. And if you carry the breast cancer enhancing variant of BRCA1, you will make sure to get frequent mammograms and MRIs and perhaps you will even choose to have prophylactic mastectomies. But what if the genetic tests give you information that amounts to a death sentence? That it turns out that there is nothing much you can do to avert your pre-ordained doom? In a sense, we all are already in that situation because right now sooner or later death is inevitable.
However, some ethicists and physicians argue that genetic testing should not be made widely available because there are so few effective medical treatments. They claim that letting people know more about the health risks they face will turn them into a bunch of miserable hypochondriacs. In other words, they believe that genetic ignorance is bliss. And many people apparently agree with the naysayers. Katharine Moser is unusual since only about 20 percent of people who are at risk of Huntington's Disease get tested. I believe that Moser made the right choice. Knowledge is power. Moser may not be able to do much about preventing the onset of HD, but she can arrange her life now to be as fulfilling and interesting as possible. She will not postpone vacations, education, visits with friends, and career plans. Because of her genetic knowledge, Moser has put her life into overdrive.
Genetic testing and other biomedical advances will some day provide all of us with a great deal more knowledge about when our lives are going to end. So here's the question: assuming that future genetic testing, combined with a sophisticated biochemical analysis of your past environmental insults, could accurately narrow your life expectancy down to a specific number of years, would you want to know how long you have left? I answer unequivocally, yes. I really want to know (barring accidents) if I'm going to live only 23 years or 41 more years, or even worse, if I'm going to drop dead in the next year. Attempts to restrict access to predictive genetic tests on paternalistic grounds must be strenuously resisted. In the near future, you will not only know that the Pale Rider is headed your way, you'll also have a pretty good idea when he will show up.
Disclosure: Because of my robust thanatophobia I have already availed myself of whole batteries of modern biomedical tests (very few genetic) including a 64-slice heart scan, a whole body MRI scan, a variety of blood tests including ones for homocysteine, C-reactive protein, glucose resistance and prostate specific antigen, a sonogram to check for gallstones, and colonoscopies (during which a polyp was removed). I have asked my physician to let me know when tests for APOE alleles and Chagas' disease become commercially available. And rather than let insurance companies decide what tests I can and cannot have, I paid out-of-pocket for many of them. I am happy to report that the 64-slice heart scan showed that, contrary to claims made by some critics, I actually do have a heart, and it's in remarkably good shape. Rumors that I am in the pay of Big Testing are false. Finally, the death clock says that I will die on September 4, 2027.
Ronald Bailey is Reason's science correspondent. His book Liberation Biology: The Scientific and Moral Case for the Biotech Revolution is now available from Prometheus Books.
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