One of the most exciting biomedical research innovations that will
likely become routine in the next decade is "gene therapy."
The process is complicated, but basically it involves the
introduction of a gene into a human cell and the transfer of that
cell into the live human body to function for the lifetime of the
Thus, one could think of it as a "very long-acting pill."
How is gene therapy done? There are several approaches, but most
rely on inserting a piece of foreign DNA (usually human, and usually
the "normal gene") into a human cell in the laboratory. Most of the
systems use a viral "vector." For instance, if we wanted to restore
a defective gene in liver cells, we might take a liver biopsy from a
patient, grow the liver cells in tissue culture outside the body,
then infect the liver cell with a virus that is known to infect liver
cells. The virus, however, would be genetically manipulated so that
it carries the "extra gene" into the cell.
With the gene now permanently in the liver cell, we would hope
that when we reintroduce the liver cells from culture back into the
patient, a "new" liver would be grown from the genetically altered
For example, a patient has a defect in cholesterol metabolism,
i.e., the cholesterol is metabolized in the liver. With gene
therapy, one could "fix" the problem.
There are other approaches. A virus could be used that is known
to infect most humans (like adenovirus, which can cause the common
cold). A scientist would engineer a specific gene into the
adenovirus and simply infect the patient. Once the cells lining the
throat were infected with the altered virus, the cells would send the
virus throughout the body, carrying the altered gene.
Other diseases would be the first targets. Gene therapy has
already been used with some success in diseases that have the
First and foremost, they must be "single gene defects," that is,
the cause of the disease must be the abnormality of a single gene.
Many diseases fall into this category, especially pediatric
immunodeficiency diseases such as cystic fibrosis and sickle cell
anemia. These diseases are caused by a mutation in a single gene,
and the loss of the function of the protein that is encoded by that
gene results in disease.
And the future? Once the single gene defect systems are routine,
more complex genetic diseases will be tackled, such as both forms of
diabetes (types I and II), Alzheimer's disease, obesity and coronary
artery disease. These diseases differ from the group listed in the
paragraph above in that more than one gene is associated with the
disease. This creates a more complex scenario for the gene