Based on a presentation from the Millennium Festival of Medicine

As a result of the revolution in the biological sciences following the development of recombinant DNA technology and the sequencing of most of the human genome, the role of genetics in the pathogenesis of human disease now dominates biomedical research. There is every sign that the rapidly evolving technology of the post genome era will unravel the function of the human genome and explain how the 50 000 to 100 000 genes interact with one another and the environment to make us what we are.

The central question for the medical sciences is the extent to which it will be possible to relate events at the molecular level with the clinical findings or phenotypes of patients with particular diseases. This problem will permeate every aspect of medical research and practice in the future. It will dominate predictive genetics and genetic counselling. It will also be of major importance for clinical decision making as new and novel approaches to the treatment of disease become available, particularly those involving genetic manipulation. Further exploration of the genome may also provide information on some of the common killers of Western society, such as heart disease, stroke, diabetes, and psychiatric disease, leading to a new form of pharmacology in which drugs are tailored to an individual's genetic make up. Even more important, and certainly more complex, will be relating genotype to phenotype. Many of our most important diseases almost certainly reflect varying susceptibility, due to the action of many different genes and a wide variety of environmental factors and to the ill understood biology of ageing.

Is there any way of guessing the likely levels of complexity that will be encountered as the genetic basis of disease is explored with the new technology? Theoretically, monogenic …