17-02-2011, 10:42 AM
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GENE THERAPY
It is an approach to treat, cure, or ultimately preventdisease by changing the expression of a person’s genes.
Gene therapy is mostly experimental, and most human trials areonly in the research stages.
Gene therapy can be targeted to somatic or germ cellsIn somatic gene therapy the recipient’s genome is changed, but the change is not passed along to the next generation.
In germline gene therapy, the parent’s egg or sperm cells are changed with the objective of passing on the changes to the offspring. It’s not currently used in humans or larger animals
Hurdles in gene therapy.
1. Gene delivery tool. The new gene/s are inserted into the bodyvia vehicles called vectors (gene carriers) which delivertherapeutic genes to the patients’ cells.The most common vectors are viruses. Scientists are trying to manipulate the viral genome to remove the disease-causing genesand introduce therapeutic genes. Viruses introduce potential otherproblems in the body, such as toxicity, immune and inflammatory responses, and gene control and targeting issues.
Alternatives being considered are complexes of DNA with lipids andproteins.
Researchers are also experimenting with introducing a 47thartificial chromosome to the body. It would exist autonomously along side of the other 46, not affecting their workings or causing any mutations. It would be a large vector capable of carrying substantial amounts of genetic information and the body’s immunesystem would not attack it.
2. Understanding gene function
Of the estimated 30-50,000 genes, we know the function of a very few.
Attempting gene therapy with out knowing how everything works could address only some of the genes implicated in particular diseases.
Likewise, genes may have more than one function.
Example. Sickle cell anemia
It’s caused by a mutation in the gene for hemoglobin. The disease manifests itself only when two copies of the mutated gene is inherited.People with only one copy of the mutated gene not only are healthy,
but they are more resistant to malaria, which is endemic in some areas of Africa. The mutation originated several thousands of years ago in parts of Africa, the Mediterranean basin, Middle East and India. Because of the survival advantage the mutation was passed along through generations.
Though, as yet, there is no cure for SCA, a combination of fluids, painkillers, antibiotics and transfusions are used to treat symptoms and complications. Hydroxyurea, an antitumor drug, has been shown to be effective in preventing painful crises. Hydroxyurea induces the formation of fetal Hb (HbF), a Hb normally found in the fetus or newborn which, when present in individuals with SCA, prevents sickling.
A mouse model of SCA has been developed and is being used to evaluate the effectiveness of potential new therapies for SCA.
How would you design a gene therapy targeting the HBB gene?
3. Multigene disorders. Most genetic disorders involve more than one gene, so inheritance of one particular gene does not mean that you have 100% chances of developing that disorder.
The particular environment (diet, smoking habits, exercise, exposure)also has a big impact on disease development.
4. High cost associated with developing this technology, and regulations associated with human experimentation
Genetic therapy ….more in depth
The goal is usually to supply cells with healthy copies of missing or altered genes. It’s an alternative to drugs.It can also be used as a way to change how a cell functions: by stimulating the immune system cells to attack cancer cells or by introducing resistance to some viruses (e.g. HIV)
