Presymptomatic testing for genetic diseases of later life. Pharmacoepidemiological considerations.

As the Human Genome Project gathers speed, new disease genes are rapidly being found. Important as these discoveries are, they are only the beginning of the process of characterising, diagnosing and treating genetic diseases. We now have the potential to predict the onset of many disorders before the appearance of clinical symptoms, even though treatment is not always available. In this review we have used a number of examples to illustrate various aspects of the presymptomatic diagnosis of genetic disease and, where possible, late-onset disorders have been chosen as examples. When treatment is available, the diagnosis of a disease before appearance of symptoms can greatly improve the prognosis. When treatment is not available, reasons to undergo presymptomatic testing may not be so obvious. However, appropriate lifestyle changes or medical surveillance can sometimes delay onset or decrease severity of a disorder. Even if no treatment is available, genetic testing and counselling for the patient and family members can provide useful information for future planning.