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By gene therapy is meant the transfer of genetic material for the purpose of preventing or curing any disease.
In the case of genetic disorders in which a gene is defective or absent, gene therapy consists of transferring the functional version of the gene to the disease-bearing organism in order to repair the defect. This is a very simple idea, but as we will see its practical realization presents several obstacles.
First step: gene isolation.
a gene is a portion of DNA that contains the information needed to synthesize a protein. To transfer a gene is to transfer a particular piece of DNA. Therefore, it is necessary first of all to have “the right piece” in hand.
The known genetic diseases are around 5000, each caused by a different genetic change. The first step in gene therapy is to identify the gene responsible for the disease. Subsequently, by molecular biology techniques it is possible to acquire a piece of DNA containing this gene. This first step is called gene isolation or cloning.
Any disease is a candidate for gene therapy as long as the gene is isolated for transfer. Thanks to the progress of molecular biology this first step is relatively simple compared to a few years ago. It has been possible to isolate numerous genes that cause genetic diseases and if others are discovered each week.
See more about this in cloning!
In vivo or in ex vivo?
These conditions show what the purpose of gene transfer is. Gene therapy procedures in vivo consist of transferring DNA directly to the patient's cells or tissues.
In the procedures ex-alive, DNA is first transferred to cells isolated from an organism, previously grown in the laboratory. The isolated cells are thus modified and can be introduced into the patient. This method is indirect and time consuming, but offers the advantage of better transfer efficiency and the ability to select and enlarge modified cells prior to reintroduction.
DNA transfer procedures in vivo or in ex-alive They have the same purpose: the gene must be transferred into cells, and once inserted it has to withstand a long time. At this time, the gene has to produce large amounts of protein to repair the genetic defect. These characteristics can be summed up in one concept: the foreign gene must effectively express itself in the host organism.
The simplest system would of course be inject DNA directly into the cells or tissues of the organism to be treated. In practice, this system is extremely ineffective: naked DNA has almost no effect on cells. In addition, this attempt requires injection into a single cell or cell groups of the patient.
For this reason, almost all current techniques for the transfer of genetic material involve the use of vectors, to transport DNA to host cells.