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For the safety of gene therapy, the
Weismann barrier is fundamental in the current thinking.
Soma-to-germline feedback should therefore be impossible.
However, there are indications that the Weissman barrier can be
breached. One way it might possibly be breached is if the treatment
were somehow misapplied and spread to the testes and therefore would
infect the germline against the intentions of the therapy.
Some of the problems of gene therapy
include:
- Short-lived nature of
gene therapy - Before gene therapy can become a permanent cure
for any condition, the therapeutic DNA introduced into target
cells must remain functional and the cells containing the
therapeutic DNA must be long-lived and stable. Problems with
integrating therapeutic DNA into the genome and the rapidly
dividing nature of many cells prevent gene therapy from
achieving any long-term benefits. Patients will have to undergo
multiple rounds of gene therapy.
- Immune response -
Anytime a foreign object is introduced into human tissues, the
immune system is designed to attack the invader. The risk of
stimulating the immune system in a way that reduces gene therapy
effectiveness is always a potential risk. Furthermore, the
immune system's enhanced response to invaders it has seen before
makes it difficult for gene therapy to be repeated in patients.
- Problems with viral
vectors - Viruses, while the carrier of choice in most gene
therapy studies, present a variety of potential problems to the
patient --toxicity, immune and inflammatory responses, and gene
control and targeting issues. In addition, there is always the
fear that the viral vector, once inside the patient, may recover
its ability to cause disease.
- Multigene disorders -
Conditions or disorders that arise from mutations in a single
gene are the best candidates for gene therapy. Unfortunately,
some of the most commonly occurring disorders, such as heart
disease, high blood pressure, Alzheimer's disease, arthritis,
and diabetes, are caused by the combined effects of variations
in many genes. Multigene or multifactorial disorders such as
these would be especially difficult to treat effectively using
gene therapy.
- Chance of inducing a
tumor - If the DNA is integrated in the wrong place in the
genome, for example in a tumor suppressor gene, it could induce
a tumor.
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