Genetic testing has pluses -- and minuses

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LEON NEAL / AFP / GETTY IMAGES ARCHIVES Patients should not jump to conclusions based on what genetic testing reveals. (CNS AFP/GETTY IMAGES)

It's been said that "all would be well if there were no 'buts.' " Unfortunately, in genetics there are many "buts" and unwary traps for unsuspecting medical consumers. So if you have the choice to receive genetic testing, be sure you know these pros and cons.

There's no doubt genetic testing is a huge benefit under certain conditions. For instance, when this subject is discussed, most people think positively about genetic screening to diagnose a child destined to be born with Down syndrome.

Genetic testing is also of great value for the parent with a dominant gene for Huntington's chorea, a severe nervous affliction. In this case, there's a 50 per cent chance a child will inherit this condition.

It would also be madness to bury your head in the sand when there is a genetic family history of colon cancer. By being aware that a faulty gene is present, regular colonoscopies can save lives by detecting polyps long before they become malignant. So, on the surface, it appears that finding these problems is a good thing. It's like the Holiday Inn TV ad that promises "No surprises."

But what about the "buts?" A report in the Canadian Medical Association Journal points out the other side of the coin. Dr. James Evans, professor of genetics at the University of North Carolina in Chapel Hill, says, "We rarely in medicine do unalloyed good. Some of the tools we employ are blunt, so you had better have great information before you employ them."

For instance, screening can detect types of breast cancer that will become invasive in some women but not in others. The trouble is there's no way of knowing which group a patient will fall into. It reminds me of what a Jewish friend who owned a department store once said to me: "My problem is that half of my advertising is worthless. But I don't know what half."

So the downside is that many women will be subjected to surgery or radiation because it is not known who needs to be treated. It's the price some women pay for having this genetic test. Some will be over-diagnosed and some over-treated.

Then suppose you are a 25-year-old woman who discovers she has a gene that will cause breast cancer. Currently, it's impossible for the gene to pinpoint the date. So should she have both breasts removed when this cancer might not appear until she is 80?

Screening also leads to incidental findings, the spotting of genetic markers that were not intended to be part of the goal. For example, the test may spot a generic defect for which there is no known treatment. How many people would want to know they are destined to develop Alzheimer's disease before there is a cure for it?

To ask these questions is like asking, "How many angels can dance on the head of a pin?" At the moment, there are no ultimate answers.

Things get even more complicated when dealing with chronic disorders such as heart disease, diabetes and osteoporosis. In these cases, more than one gene might be involved, and it's still unknown how much depends on genetics and how much on environment and lifestyle.

Today, more people are ill due to faulty lifestyle than faulty genes. For instance, the gene for Type 2 diabetes may not trigger this disease if there's no weight gain. And if a gene is discovered for osteoporosis, it's possible that brittle bones could be averted by ensuring an adequate dietary intake of calcium, vitamin D and vitamin K2.

So don't jump to the hasty conclusion that coronary attacks of several relatives were caused by a generic abnormality. You may be right if they had all behaved themselves. But you had better check first to see if they were all overweight, smoked two packs of cigarettes a day and were couch potatoes for years.

You might discover that Pogo was right: "We have discovered the enemy, and the enemy is us." All too often today, we are the architects of our own misfortune, not our genes.

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Republished from the Winnipeg Free Press print edition July 6, 2012 A21