Genetic Counseling & The Future

I hope you have now gained some appreciation of how important genes are for your habitus, health, and happiness, and how paying attention to your family tree may tell you something, though of course not everything, about your own genes and health prospects. Sir William Osler advised us to choose our parents wisely, but not only are you unable to choose your parents, but you cannot choose which of their genes you draw. You get only half of your mother's genes and half of your father's. This is why you resemble your parents and sibs in some respects but not others.

You have also seen that genes do not determine our characteristics by themselves—environmental factors are important too. Although you have no control over the assortment of parental genes that fate dealt you, you do have at least some control over your lifestyle and that of your children. This book has aimed at helping you see how to adjust your lifestyle to guard against the particular risks that your family tree says you are sujbect to.

A recurrent theme of the book is that the common familial disorders are caused by a combination of several genes, each with a small effect, and several environmental factors. Each one increases your susceptibility to the disorder, and if you draw enough of them, you get sick. Because each factor has a relatively small effect, they are hard to sort out, identify, and measure.

The new techniques of DNA technology are identifying more and more mutant genese that contribute to disease. Most of them are those with a major effect, because they are easier to find. They cause diseases showing Mendelian inheritance, and most are so rare that you have probably never heard of them; they are beyond the scope of this book. It is more difficult to identify the mutant genes of small effect that contribute to susceptibility for the common familial disorders. But more and more of these are also being identified. Furthermore, techniques for detecting the mutant genese will become less expensive. There are now micro-arrays that make it possible to test a thousand or more of a person's genes on a chip no bigger than your thumb nail!

Researchers are pursuing not only the susceptibility genes for the common disorders, but also the environmental factors with which they interact. There are several ongoing studies in which tens of thousands of families are typed for thousands of genes, and also for hundreds of factors in their environments. These families are then followed for many years to see what diseases they develop. In this way, the connections between diseases, genes, and environments will be unraveled, but it will take many years.

Some enthusiasts foresee a world in which everyone will be screened at birth for thousands of genes, that will tell us not only which diseases we will surely develop (hemophilia, sickle-cell anemia, Huntington disease), but also what diseases we will be susceptible to if we choose the wrong lifestyle, and which drugs we shoudl take when we do get a disease. As the Bard might have written, O brave new world that hath such wonders in it!

But geneticists are beginning to think that this view is a bit unrealistic. We already offer testing for many genes, such as the Huntington disease gene, and the BRCA gene for breast cancer, but only to people with high risk, who have received genetic counseling before and after testing. Whether to be tested is not a simple decision. Some people choose not to be tested; they prefer not to know. For both ethical and economic reasons, genetic testing is not likely ever to be done on a population-wide basis.

Testing for mutant genes will be useful for predicting how we will react to drugs, and for increasing our understanding of disease. But, for a long time, the best indicator of what diseases we are susceptible to, and what lifestyle will guard against them, will be our family histories. Know your family tree!