Medical Consequences of the Human Genome Project
Rossiter, Belinda F. J., Caskey, Thomas C., National Forum
The Human Genome Project has the potential for rapid discovery of the estimated 4,000 disease genes thought to reside within the human genome and for improved techniques with which to investigate them. The first stage in unraveling the mechanism of an inherited disorder is discovery of the appropriate gene, which then permits detection of disease-causing mutations within the gene and development of DNA-based diagnostic procedures. Isolation of a disease gene permits study of the structure and function of its normal protein product and leads to better understanding of the disease that results from a missing or altered protein. Further knowledge of the gene's product and disease mechanism may lead to improved medical strategies or development of more effective drugs. The delivery of a functional gene to the appropriate tissue so that an inherited or acquired defect is corrected is called gene therapy. Notable examples of recently isolated disease genes include those responsible for fragile X syndrome (the most common cause of inherited mental retardation) and myotonic dystrophy (the most common adult muscular dystrophy).
The benefits of these new genetic discoveries are accompanied by difficult ethical issues. If carriers for a common disorder (such as cystic fibrosis) can be detected, should the population as a whole be screened? If there are people who are unaffected themselves but who have a high risk of bearing affected children (as happens in families with fragile X syndrome and myotonic dystrophy), should these people be identified? Can they be advised not to have children? In what circumstances should individuals at risk for an adult-onset disease (such as adult polycystic kidney disease) be tested before symptoms appear? Who should have access to test results? Most of these problems stem from the fact that discovery of a disease gene leads very quickly to improved diagnostic procedures, although treatment or cures may not be available for many more years. This article will briefly describe the Human Genome Project and elaborate on progress made in the particular disorders mentioned above.
The Human Genome Project. The Human Genome Project officially started in 1990 and is estimated to last fifteen years at a total cost of $3 billion. Funding in the United States is provided primarily by the National Institutes of Health and the U.S. Department of Energy. The project has two main objectives: to develop detailed maps of the human genome (genetic makeup) and the genomes of other well-studied organisms, such as bacteria, fruit flies, and mice; and to determine the order (sequence) of the individual nucleotides in the DNA of these genomes. The second goal will be attempted only if it can be done at a reasonable cost. Progress in the generation of genome maps has been encouraging, and the short-term (five-year) goals set for the project are likely to be achieved. The development of computer databases, software tools, and mechanisms of communication is critical to the success of the project. Part of the budget for the Human Genome Project has also been set aside for discussion of social, legal, and ethical implications of the new discoveries, some of which are mentioned below.
Cystic Fibrosis. Cystic fibrosis is an autosomal recessive disorder affecting approximately 1 in 2,500 Caucasians, which means that in this population about 1 in 25 people is an unaffected carrier of a cystic fibrosis mutation. The child of two carriers has a one-in-four chance of inheriting a mutation from each parent and thus being affected with cystic fibrosis. When the gene causing this disease was discovered in 1989, it was also found that one particular mutation was present on about 70 percent of cystic fibrosis chromosomes but never on a normal one. It was initially hoped that there would be only a few other mutations, but this has not proved to be the case. The Cystic Fibrosis Genetic Analysis Consortium, a network of 88 laboratories around the world, has already described more than 170 different mutations in the cystic fibrosis genes of affected individuals. …