A gene is defined as a stretch of DNA (deoxyribonucleic acid) that contains nucleotide sequences. Based on them, specific proteins are synthesized, which in turn, are responsible for the expression and functions of body cells and tissues. If there is any alteration in the genetic sequence, the protein synthesis is disturbed. In such a condition, the cells and tissues are unable to perform their normal function, leading to genetic diseases.
This therapy is a scientific technique, by which a segment of a nucleotide sequence is inserted into an individual's cell, for the purpose of treating diseases. Its main principle is to restore the normal functioning of cells and tissues, by replacing abnormal or mutated genes. In simple terms, it is a method of correcting defective genes. There are several ways of implementing this technique; inserting a normal gene into the genome to replace a defective one, and changing the regulation for expression of a specific gene. Another method is to apply selective reverse mutation, so that the defective gene returns to its original form.
In majority of cases, a normal therapeutic gene is inserted by using a vector or a carrier molecule. This vector serves the purpose of delivering the normal gene to the target cell. As it incorporates this gene in the cells (for example liver cells), it starts producing functional proteins, thus restoring the normal functions of this cell. Various types of viruses such as retrovirus and adenovirus, are used for the purpose of carrier molecules. Before using any of them, the genomic content is changed by removing the defective gene, and replacing it with a therapeutic one.
There are many potential side effects of using viruses as vectors, some of which include target-related problems, inflammatory response of the immune system, and toxicity. A more recent technique is to introduce the normal gene directly to the target cell without using vectors. Though it sounds comparatively easy, it is not applicable to all types of such cells. Another disadvantage of this method is that, it requires a large amount of DNA.
Another drawback is the short-term effectiveness of the normal gene, after introducing into the target cell. The dividing cells present in the body, are the ones that prevent the expression of therapeutic genes. It is also necessary to regulate the autoimmune responses of the body. This therapy is less effective for multigene problems (presence of many defective genes).
Though the technology of this therapy is not so advanced, in the present scenario, it has already widened the scope of medical science. All genetic disorders and most of the chronic diseases involve malfunctioning of the genes. Hence, the method given above is a promising technique for treatment of such severe health conditions. Genetic research programs are ongoing to discover treatment options for chronic medical conditions such as heart diseases, cancer, cystic fibrosis, and AIDS. Nowadays, private as well as government grants are provided, so as to encourage studies on this topic.