It is probably obvious that for most subjects the quality of understanding is limited by the quality of information. If our information is faulty, so is our understanding. Conversely, as we learn more, our understanding of processes and events will improve. The advent of shared databases, the internet, and other communication tools has given us unprecedented insight into unfolding events around the world. Similarly, advances in molecular, biochemical, and other diagnostic technologies are changing the limits of genetic testing and screening. But we must put this into an historical perspective. Molecular insights have set the foundation for recent changes in the relatively short history of technological advancement. Not long ago, resources like personalized DNA databases and targeted genetic testing were hardly even imaginable. But today, the only certain prediction about the future of individualized genomic data is that information will increase.
When considering available genetic tests, one quite reasonable question is: "why not just get the most detailed information first? Do a DNA sequence." This is, after all, the age of genomics (Figure 11-1). DNA sequencing is being applied to identify genetic variation among individuals, within population groups, and in hundreds of species throughout the animal and plant worlds. But sequencing can be comparatively expensive and time consuming. In addition, it can give more information than is really necessary to answer most clinical questions. Indeed, sometimes the mass of information can actually bury the key result.
A small portion of a large DNA microarray or "gene chip." Each of the colored spots shows binding of fluorescently-labeled cDNA made from the RNA isolated from a tissue sample. Spot color indicates the amount of binding and thus the relative amount of RNA in the original sample.
In this chapter we will explore some of the growing array of genetic tests that are currently available, although we must recognize that this field will advance rapidly as new techniques are discovered and applied. This creates a continuing challenge for physicians and genetic counselors. But that is not bad. A growing battery of analytical tools and data sources—in other words, the "information challenge"—is good news for the medical profession and for patients. Still, it means that all of us need to stay up-to-date on new advances. This chapter will focus on some of the practical aspects of testing and evaluating genetic conditions in patients. What are some of the tools available to analyze a patient's condition? What principles guide screening and interpretation? Not surprisingly, the topic of this chapter will probably change almost daily in the world of the practicing clinician.
But behind this advance in technology hides an age-old question. What does it all mean? It is not uncommon for the results of a DNA screen to report "finding of unknown clinical significance." The warning should be clear. ...