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Medicine and the New
Genetics

Genomics and Its Impact on Science and Society: The Human
Genome Project and Beyond

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Gene Testing, Pharmacogenomics, and Gene
Therapy
CadeususDNA underlies almost
every aspect of human health, both in function and dysfunction.
Obtaining a detailed picture of how genes and other DNA sequences
function together and interact with environmental factors
ultimately will lead to the discovery of pathways involved in
normal processes and in disease pathogenesis. Such knowledge will
have a profound impact on the way disorders are diagnosed, treated,
and prevented and will bring about revolutionary changes in
clinical and public health practice. Some of these transformative
developments are described below.

Gene Testing
DNA-based tests are among the first
commercial medical applications of the new genetic discoveries.
Gene tests can be used to diagnose disease, confirm a diagnosis,
provide prognostic information about the course of disease, confirm
the existence of a disease in asymptomatic individuals, and, with
varying degrees of accuracy, predict the risk of future disease in
healthy individuals or their progeny.

Currently, several hundred genetic
tests are in clinical use, with many more under development, and
their numbers and varieties are expected to increase rapidly over
the next decade. Most current tests detect mutations associated
with rare genetic disorders that follow Mendelian inheritance
patterns. These include myotonic and Duchenne muscular dystrophies,
cystic fibrosis, neurofibromatosis type 1, sickle cell anemia, and
Huntington’s disease.

Recently, tests have been developed
to detect mutations for a handful of more complex conditions such
as breast, ovarian, and colon cancers. Although they have
limitations, these tests sometimes are used to make risk estimates
in presymptomatic individuals with a family history of the
disorder. One potential benefit to using these gene tests is that
they could provide information to help physicians and patients
manage the disease or condition more effectively. Regular
colonoscopies for those having mutations associated with colon
cancer, for instance, could prevent thousands of deaths each
year.

Some scientific limitations are
that the tests may not detect every mutation associated with a
particular condition (many are as yet undiscovered), and the ones
they do detect may present different risks to different people and
populations. Another important consideration in gene testing is the
lack of effective treatments or preventive measures for many
diseases and conditions now being diagnosed or
predicted.

Revealing information about the
risk of future disease can have significant emotional and
psychological effects as well. Moreover, the absence of privacy and
legal protections can lead to discrimination in employment and
insurance or other misuse of personal genetic information.
Additionally, because genetic tests reveal information about
individuals and their families, test results can affect family
dynamics. Results also can pose risks for population groups if they
lead to group stigmatization.

Other issues related to gene tests
include their effective introduction into clinical practice, the
regulation of laboratory quality assurance, the availability of
testing for rare diseases, and the education of healthcare
providers and patients about correct interpretation and attendant
risks.

Families or individuals who have
genetic disorders or are at risk for them often seek help from
medical geneticists (an M.D. specialty) and genetic counselors
(graduate-degree training). These professionals can diagnose and
explain disorders, review available options for testing and
treatment, and provide emotional support. (For more information,
see 
Medicine and the New Genetics (http://www.ornl.gov/TechResources/Human_Genome/medicine/medicine.html))

Pharmacogenomics: Moving Away from
“One-Size-Fits-All”
Therapeutics
Within the next decade, researchers
will begin to correlate DNA variants with individual responses to
medical treatments, identify particular subgroups of patients, and
develop drugs customized for those populations. The discipline that
blends pharmacology with genomic capabilities is called
pharmacogenomics.

More than 100,000 people die each
year from adverse responses to medications that may be beneficial
to others. Another 2.2 million experience serious reactions, while
others fail to respond at all. DNA variants in genes involved in
drug metabolism, particularly the cytochrome P450 multigene family,
are the focus of much current research in this area. Enzymes
encoded by these genes are responsible for metabolizing most drugs
used today, including many for treating psychiatric, neurological,
and cardiovascular diseases. Enzyme function affects patient
responses to both the drug and the dose. Future advances will
enable rapid testing to determine the patient’s genotype and
guide treatment with the most effective drugs, in addition to
drastically reducing adverse reactions.

Genomic data and technologies also are
expected to make drug development faster, cheaper, and more
effective. Most drugs today are based on about 500 molecular
targets; genomic knowledge of the genes involved in diseases,
disease pathways, and drug-response sites will lead to the
discovery of thousands of new targets. New drugs, aimed at specific
sites in the body and at particular biochemical events leading to
disease, probably will cause fewer side effects than many current
medicines. Ideally, the new genomic drugs could be given earlier in
the disease process. As knowledge becomes available to select
patients most likely to benefit from a potential drug,
pharmaco-genomics will speed the design of clinical trials to bring
the drugs to market sooner.

Gene Therapy, Enhancement
The potential for using genes
themselves to treat disease or enhance particular traits has
captured the imagination of the public and the biomedical
community. This largely experimental field—gene transfer or
gene therapy—holds potential for treating or even curing such
genetic and acquired diseases as cancers and AIDS by using normal
genes to supplement or replace defective genes or bolster a normal
function such as immunity.

More than 600 clinical gene-therapy
trials involving about 3500 patients were identified worldwide in
2002.* The vast majority take place in the United States (81%),
followed by Europe (16%). Although most trials focus on various
types of cancer, studies also involve other multigenic and
monogenic, infectious, and vascular diseases. Most current
protocols are aimed at establishing the safety of gene-delivery
procedures rather than effectiveness.

Gene transfer still faces many
scientific obstacles before it can become a practical approach for
treating disease. According to the American Society of Human
Genetics’ Statement on Gene Therapy, effective progress will
be achieved only through continued rigorous research on the most
fundamental mechanisms underlying gene delivery and gene expression
in animals.

*Source: Journal of Gene Medicine Web site (www.wiley.co.uk),
accessed March 2003.

Primer - History - Insights -
Medicine
- Benefits - Concerns -
Beyond - Systems - Microbes - Dictionary - Home

 The online presentation of this publication is a special
feature of the Human Genome
Project Information Web site (http://www.ornl.gov/TechResources/Human_Genome/).

