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Humans have known for millennia that heredity affects health.1 However, Mendel's seminal contribution to the elucidation of the mechanisms by which heredity affects phenotype occurred less than 150 years ago, and Garrod began applying this knowledge to human health only at the start of the past century. For most of the 20th century, many medical practitioners viewed genetics as an esoteric academic specialty; that view is now dangerously outdated.
The Advent of Genomic Medicine
The recent completion of the draft sequence of the human genome2 ,3 and related developments have increased interest in genetics, but confusion remains among health professionals and the public about the role of genetic information in medical practice. Inaccurate beliefs about genetics persist, including the view that in the past it had no effect on the practice of medicine and that its influence today is pervasive. In fact, for decades knowledge of genetics has had a large role in the health care of a few patients and a small role in the health care of many. We have recently entered a transition period in which specific genetic knowledge is becoming critical to the delivery of effective health care for everyone.
If genetics has been misunderstood, genomics is even more mysterious -- what, exactly, is the difference? Genetics is the study of single genes and their effects. "Genomics,"4 a term coined only 15 years ago, is the study not just of single genes, but of the functions and interactions of all the genes in the genome. Genomics has a broader and more ambitious reach than does genetics. The science of genomics rests on direct experimental access to the entire genome and applies to common conditions, such as breast cancer5 and colorectal cancer,6 human immunodeficiency virus (HIV) infection,7 tuberculosis,8 Parkinson's disease,9 and Alzheimer's disease.10 These common disorders are also all due to the interactions of multiple genes and environmental factors. They are thus known as multifactorial disorders. Genetic variations in these disorders may have a protective or a pathologic role in the expression of diseases.
The role of genomics in health care is in part highlighted by the decreasing effect of certain environmental factors, such as infectious agents, on the burden of disease. Genomics also contributes to the understanding of such important infectious...