Buried in the cells of each newborn is a unique set of genetic instructions. These molecular blueprints not only shape how the child will grow and develop and whether it will have brown eyes or blue, but what sorts of medical problems it might encounter. In some instances the likelihood of developing such disorders as heart disease or cancer can be forecast from a child's genes. How can doctors detect them in the morass of a person's DNA to try to prevent their deadly effects? The following article, adapted from an account by scientists Stuart Orkin and Gary Felsenfeld, explores the trail of research that led scientists to answer those questions and open the door to gene testing, which is promising to transform medicine powerfully. It provides a dramatic example of how science works and how basic research leads to practical results that were virtually unimaginable when the research was done.

Beth M.'s father died of colon cancer, as did his mother. Then colon cancer was diagnosed in two of her brothers, both in their 40s. Beth, 37, felt that a curse was hanging over her family and worried about her future and that of her children. Could she have inherited from her father a tendency to develop colon cancer at an early age, just as she inherited his hazel eyes?

Fortunately for Beth, researchers have pinpointed the defective gene that has plagued her family and causes the odds of developing colon cancer to be 85% or greater. The gene is called MSH2, and researchers have developed an experimental genetic test for defects in this particular gene. Within a short time of having her blood drawn, Beth could stop worrying--the blood test showed that she did not inherit the MSH2 gene from her father. Although the test result did not free Beth from the possibility of ever developing colon cancer--the test predicts only the likelihood of developing colon cancer fostered by the MSH2 gene, and not from other causes--she now knew that the uncomfortable and expensive colon-cancer detecting procedures that she underwent each year were no longer necessary; nor was the excessive worry.

What Beth didn't know was that the simple genetic test she had for the MSH2 gene would not have been possible without more than 50 years of research by many scientists who paved the way for pinpointing the genes that foster susceptibility to specific diseases. Most of the scientists had no idea that their quest for answers to such basic questions as how yeast cells detect and repair flaws in their genetic material would lead to practical genetic tests on people like the one for the MSH2 gene. These tests are also raising ethical, social, and legal questions as they take medicine into uncharted territory.

This article is available in Japanese, and Spanish.