The Human Genome Project has made it easier to genetically map and clone mutant genes which predispose to a great many human diseases. In addition to diseases inherited in a simple Mendelian fashion, there are many degenerative and infectious diseases, and sensitivities to environmental insults, in which the genetic make-up of an individual contributes to the course of the disease. Once a gene or genes associated with disease has been cloned, it is possible to design DNA-based diagnostics to detect altered forms of the gene which predispose to disease. The ability to predict the development of disease makes possible early intervention to limit the severity of a disease or to use gene therapy to cure inherited disorders.