Roanoke Times
Copyright (c) 1995, Landmark Communications, Inc.
DATE: THURSDAY, March 24, 1994 TAG: 9403260007
SECTION: EDITORIAL PAGE: A13 EDITION: METRO
SOURCE: RALPH E. DITTMAN
DATELINE: LENGTH: Medium
Most people, even the most educated among us, don't understand the nature of the information genetic testing provides. That's why discrimination based on genetic information - the mere perception or probability that an individual might someday become ill or have a child with a serious medical problem - is a real concern.
Genetic screening is a relatively new science. Still, based on current knowledge, there is every reason to believe that a single blood test someday will be able to detect from 100 to 1,000 of the most common genetic diseases, predispositions and "risk factors."
This is where the trouble begins. Having a genetic code that indicates a predisposition to a certain disease or a higher-than-average risk of disease does not mean you will ever get that disease. Indeed, having this information may enable us to take preventive measures, ranging from prescription drugs to lifestyle changes.
That's why daily newspaper accounts proclaiming a link between disease A and gene B must be tempered with an insight into the true causes of disease.
For a majority of diseases, there is no single triggering agent, but rather a network of factors, including genetic makeup.
It may be true that certain highly hereditary cancers are the result of hereditable genetic defects. Yet, perhaps less than 1 percent of cancers occur in this category, according to Cambridge University oncologist B.A.J. Ponder, director of cancer research for the National Center for Human Genome Research.
How much cancer is due to inherited predisposition? There is no clear answer to this question. Perhaps a better way to phrase it is to ask: Which cancers have a sufficiently strong inherited predisposition to be of practical significance for prevention or treatment?
Consider the following: Scientists have identified a gene, known as BRCA 1, that appears to demonstrate a genetic link to breast cancer. In the general population, the risk of breast cancer runs about 10 percent. Among women with the BRCA 1 gene, the risk of developing breast cancer by age 55 is approximately 72 percent, and by age 80 this increases to 86 percent. With approximately one in 200 women in the United States (about 600,000 women) at risk of carrying the BRCA 1 gene, policymakers may soon be debating the cost-effectiveness of general screening for BRCA 1.
If a 55-year-old patient has the test and it is negative, so be it. But what if the test is positive and she is characterized as having a "pre-existing condition?" That could affect her ability to qualify for health insurance or even to get a job: a genetic Catch-22.
In the broad sense, all cancers are genetic, involving the runaway replication of cellular tissue. Identification would not act in this fashion. Identification of oncogenes - those tiny portions of the human genetic code which, when mutated, can produce cancer - and tumor suppressor genes - whose damage or impairment allows a malignancy to grow - has dramatically increased our knowledge of cancer. But it has not demonstrated that cancer is inheritable.
This is the key point to keep in mind as we see disease after disease, risk factor after risk factor, predisposition after predisposition linked to gene after gene, day after day, newspaper story after newspaper story.
The major causes of cancer remain personal habits such as smoking or overexposure to sunlight, occupational exposure and dietary factors. Lung cancer death rates for U.S. men rose from 5 per 100,000 in 1930 to 75 per 100,000 in 1985; for women, from 3 per 100,000 to 28 per 100,000. Inheritable genetic propensities have little to do with such increases.
Ralph E. Dittman, M.D., is a surgeon in Houston, Texas. This article is excerpted from Priorities, the quarterly journal of the American Council of Science and Health.
by CNB