The International HapMap Project will benefit human health by providing an extensive resource that researchers can use to discover the genetic variants involved in disease and individual responses to therapeutic agents. Once such variants have been discovered, researchers can learn much more about the origins of illnesses and about ways to prevent, diagnose, and treat those illnesses.

The goal of the Project is not to identify these disease-related genes directly. Rather, by identifying haplotypes, the HapMap provides a tool that can be used in what are called association studies. For these studies, researchers will compare the haplotypes in individuals with a disease to the haplotypes of a comparable group of individuals without a disease (the controls). If a particular haplotype occurs more frequently in affected individuals compared with controls, a gene influencing the disease may be located within or near that haplotype.

Common diseases such as cancer, stroke, heart disease, diabetes, depression, and asthma usually result from the combined effects of a number of genetic variants and environmental factors. According to an idea known as the common disease-common variant hypothesis, the risk of contracting common diseases is influenced by genetic variants that are relatively common in populations. Not enough data are yet available to evaluate the generality of this hypothesis, but more and more widely distributed genetic variants associated with common diseases are being discovered, including variants that contribute to autoimmune diseases, schizophrenia, diabetes, asthma, stroke, and heart attacks. One of the many benefits of the International HapMap Project will be the use of the HapMap to learn more about the links between these common disorders and our genes.

Knowledge derived from use of the HapMap also will result in advances that are difficult to predict today. Medical treatments could be customized, based on a patient's genetic make-up, to maximize effectiveness and minimize side effects. Genetic variants contributing to longevity or resistance to disease could be identified, leading to new therapies with widespread benefits. As with any new body of knowledge, the HapMap is likely to lead to both new challenges and to unexpected and unprecedented opportunities.