Gene therapy is when DNA is introduced into a patient to treat a genetic disease. The new DNA usually contains a functioning gene to correct the effects of a disease-causing mutation.
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The DNA is carefully selected to correct the effect of a mutated gene that is causing disease. The technique was first developed in 1972 but has, so far, had limited success in treating human diseases. There are two different types of gene therapy depending on which types of cells are treated: Somatic gene therapy: transfer of a section of DNA to any cell of the body that doesn’t produce sperm or eggs. Effects of gene therapy will not be passed onto the patient’s children. Germline gene therapy: transfer of a section of DNA to cells that produce eggs or sperm. Effects of gene therapy will be passed onto the patient’s children and subsequent generations.
Gene therapy techniques
There are several techniques for carrying out gene therapy. These include:
Gene augmentation therapyThis therapy adds DNA containing a functional version of the lost gene back into the cell. The new gene produces a functioning product at sufficient levels to replace the protein that was originally missing. This is only successful if the effects of the disease are reversible or have not resulted in lasting damage to the body. For example, this can be used to treat loss of function disorders such as cystic fibrosis by introducing a functional copy of the gene to correct the disease (see illustration below).
Gene inhibition therapySuitable for the treatment of infectious diseases, cancer and inherited disease caused by inappropriate gene activity. The aim is to introduce a gene whose product either: inhibits the expression of another gene interferes with the activity of the product of another gene. The basis of this therapy is to eliminate the activity of a gene that encourages the growth of disease-related cells.
Killing of specific cellsSuitable for diseases such as cancer that can be treated by destroying certain groups of cells. The aim is to insertDNA into a diseased cellthat causes that cell to die. This can be achieved in one of two ways: the inserted DNA contains a “suicide” gene that produces a highly toxic product which kills the diseased cell the inserted DNA causes expression of a protein that marks the cells so that the diseased cells are attacked by the body’s natural immune system. It is essential with this method that the inserted DNA is targeted appropriately to avoid the death of cells that are functioning normally.
How is DNA transfer done?The vector acts as a vehicle to carry the new DNA into the cells of a patient with a genetic disease. Once inside the cells of the patient, the DNA/gene is expressed by the cell’s normal machinery leading to production of the therapeutic protein and treatment of the patient’s disease.
An illustration to show the transfer of a new gene into the nucleus of a cell via a viral vector.Imagecredit:GenomeResearchLimited
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