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Biotechnology Gene Therapy
Until the advent of gene therapy, it was only possible to suppress the symptoms of inherited disease.
Only a small proportion of those affected were able to lead fully active lives. Gene therapy is the
attempted repair or replacement of disease-causing genes by the introduction of functional genes. In
this way doctors hope to treat many inherited diseases effectively for the first time. The startling
rapidity with which gene therapy has developed stems from two factors:
A much improved understanding of the molecular basis of many diseases,
The development of techniques to isolate selected genes of interest and to study and change
them outside the body.
Unlike conventional treatments, which attempt to deal with the consequences of a defect, gene therapy
aims to correct the defective gene itself. Gene therapy introduces new genes into the body cells. Two
quite separate types of gene therapy can be envisaged:
Germ-line therapy - where the modifications affect the inherited genetic material of sex cells
and are passed onto future generations.
Somatic gene therapy - where genes are introduced to ordinary body cells. However, in this
case, the sex cells are not altered in any way and the genetic modification cannot be passed
onto future generations.
GENE THERAPY TRIALS BEGIN
Gene therapy trials have been given the go-ahead by medical authorities in many countries. Although
this work is still in its infancy, the early results of some trials are encouraging.
The modern era of gene therapy began in the USA, in 1990, with the extremely rare but incurable
immunodeficiency, ADA (adenosine deaminase) deficiency. Patients with ADA deficiency do not develop
an immune system, so cannot fight infections; they need constant protection from pathogens. Two
children were given a working copy of the ADA gene, which was inserted into some of their white blood
cells. Five years on, these children are living comparatively normal lives. This example shows that new
genes can be introduced into human cells, replacing missing function.
Nevertheless, because the modified cells eventually die, the treatment has to be repeated at regular
intervals. Manipulation of stem cells could overcome this problem, since unlike most body cells, they
continue to divide throughout life. By replacing old, worn out cells in the bone marrow, for example,
they constantly replenish the body's circulating blood cells. If these cells could be corrected by gene
therapy, they would provide a life-long supply of the correct protein.
ADA deficiency is extremely rare - only about a dozen people have been treated this way. But more
than 200 trials of different gene therapy have been approved in recent years. Most are cancer trials,
though gene therapies for cystic fibrosis and heart diseases have also been attempted. So far the
results have not been very positive but it is still early days.
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APPLICATIONS OF GENE THERAPY
Gene therapy covers a range of techniques and is potentially applicable both to:
Single gene disorders - caused by a single absent or malfunctioning gene,
Multi-factorial diseases - where environmental factors as well as genes contribute to