Gene therapy carries the promise of cures for many diseases and for types of medical
treatment that didn't seem possible until recently. With its potential to eliminate
and prevent hereditary diseases such as cystic
fibrosis and hemophilia and its use as a possible cure for heart disease, AIDS,
and cancer, gene therapy is
a potential medical miracle-worker.
But what about gene therapy for children? There's a fair amount of risk involved,
so thus far only seriously ill kids or those with illnesses that can't be cured by
standard medical treatments have been involved in clinical trials using gene therapy.
As those studies continue, gene therapy may soon offer hope for children
with serious illnesses that don't respond to conventional therapies.
Our genes help make us
unique. Inherited from our parents, they go far in determining our physical traits
— like eye color and the color and texture of our hair. They also determine
things like whether babies will be male or female, the amount of oxygen blood can
carry, and the likelihood of getting certain diseases.
Genes are composed of strands of a molecule called DNA and are located in single
file within the chromosomes. The genetic message is encoded by the building blocks
of the DNA, which are called nucleotides. Approximately 3 billion pairs of nucleotides
are in the chromosomes of a human cell, and each person's genetic makeup has a unique
sequence of nucleotides. This is mainly what makes us different from one another.
Scientists believe that every human has about 25,000 genes per cell. A mutation,
or change, in any one of these genes can result in a disease, physical disability,
or shortened life span. These mutations can be passed from one generation to another,
inherited just like a mother's curly hair or a father's brown eyes. Mutations also
can occur spontaneously in some cases, without having been passed on by a parent.
With gene therapy, the treatment or elimination of inherited diseases or physical
conditions due to these mutations could become a reality.
Gene therapy involves the manipulation of genes to fight or prevent diseases. Put
simply, it introduces a "good" gene into a person who has a disease caused by a "bad"
Two Types of Gene Therapy
The two forms of gene therapy are:
Somatic gene therapy, which involves introducing a "good" gene
into targeted cells to treat the patient — but not the patient's future children
because these genes do not get passed along to offspring. In other words, even though
some of the patient's genes may be altered to treat a disease, it won't change the
chance that the disease will be passed on to the patient's children. This is the more
common form of gene therapy being done.
Germline gene therapy, which involves modifying the genes in
egg or sperm cells, which will then pass any genetic changes to future generations.
Experimenting with this type of therapy, scientists injected fragments of DNA into
fertilized mouse eggs. The mice grew into adults and their offspring had the new gene.
Scientists found that certain growth and fertility problems could be corrected with
this therapy, which led them to think that the same could be true for humans. Although
it has potential for preventing inherited disease, germline gene therapy is controversial
and very little research is being done, for technical and ethical reasons.
Possible Effects of Gene Therapy
Currently, gene therapy is done only through clinical
trials, which often take years to complete. After new drugs or procedures are
tested in laboratories, clinical trials are conducted with human patients under strictly
controlled circumstances. Such trials usually last 2 to 4 years and go through several
phases of research. In the United States, the U.S. Food and Drug Administration (FDA)
must then approve the new therapy for the marketplace, which can take another 2 years.
The most active research being done in gene therapy for kids has been for genetic
disorders (like cystic fibrosis). Other gene therapy trials involve children with
severe immunodeficiencies, such as adenosine deaminase (ADA) deficiency (a rare genetic
disease that makes kids prone to serious infection), sickle cell anemia, thalassemia,
hemophilia, and those with familial hypercholesterolemia (extremely high levels of
Gene therapy does have risks and limitations. The viruses and other agents used
to deliver the "good" genes can affect more than the cells for which they're intended.
If a gene is added to DNA, it could be put in the wrong place, which could potentially
cause cancer or other damage.
Genes also can be "overexpressed," meaning they can drive the production of so
much of a protein that they can be harmful. Another risk is that a virus introduced
into one person could be transmitted to others or into the environment.
Gene therapy trials in children present an ethical dilemma, according to some gene
therapy experts. Kids with an altered gene may have mild or severe effects and the
severity often can't be determined in infants. So just because some kids appear to
have a genetic problem doesn't mean they'll be substantially affected by it, but they'll
have to live with the knowledge of that problem.
Kids could be tested for disorders if there is a medical treatment or a lifestyle
change that could be beneficial — or if knowing they don't carry the gene reduces
the medical surveillance needed. For example, finding out a child doesn't carry the
gene for a disorder that runs in the family might mean that he or she doesn't have
to undergo yearly screenings or other regular exams.
The Future of Gene Therapy
To cure genetic diseases, scientists must first determine which gene or set of
genes causes each disease. The Human Genome Project and other international efforts
have completed the initial work of sequencing and mapping virtually all of the 25,000
genes in the human cell. This research will provide new strategies to diagnose, treat,
cure, and possibly prevent human diseases.
Although this information will help scientists determine the genetic basis of many
diseases, it will be a long time before diseases actually can be treated through gene
Gene therapy's potential to revolutionize medicine in the future is exciting, and
hopes are high for its role in ;curing and preventing childhood diseases. One day
it may be possible to treat an unborn child for a genetic disease even before symptoms
Scientists hope that the human genome mapping will help lead to cures for many
diseases and that successful clinical trials will create new opportunities. For now,
however, it's a wait-and-see situation, calling for cautious optimism./p>