Gene therapy is a technique or method used to replace the non-functional or mutated form of genes with fully functioning, normal gene. Non-functional genes are the one which will produce abnormal proteins, after transcription and translation process. These abnormal proteins will not function normally, causing some kind of abnormality or genetic disease. This type of disability or genetic disorders can be treated with the normal genes sent into the patient's body. These normal functional genes are sent into the nucleus of a cell, with the help of viral vector. The main problems with gene therapy are it's a very complex technology; theoretically which is very easy to understand but very difficult in practice. And also our expectations from this technology is too high, we expect that gene therapy is answer for all the genetic disorders.
Scientists and researchers are finding new ways of gene therapy using human genetic engineering technology. DNA scissors and exon-skipping gene therapy are the two novel techniques discovered by the researchers.
Exon-skipping Gene Therapy:
First what is an exon? Genes which code for a protein are divided into two regions, known as exons and introns. DNA sections which code for the protein are known as exons, and the portions of DNA which are present in between these exons are known as introns. Introns do not code for protein as such.
Exon-skipping gene therapy is a promising technique to scientists to treat and cure Duchenne Muscular Dystrophy (DMD), an X-linked recessive form of genetic disorder. Exon-skipping technology is designed so brilliantly that it skips over the genes which are mutated, in other words this technique completely ignores the mutated genes.
Mutation of the gene called as dystropin which is present on the X-chromosome induces a genetic condition or disorder known as Duchenne Muscular Dystrophy. Dystropin is a very long gene and mutated form of this gene does not produce the protein dystropin which plays a very important role in muscle strength and stability.
In a new technique of gene therapy, instead of targeting the mutated form of gene and replacing it with the functional gene, it is ignored. That is the aimof the exon-skipping gene therapy is to activate and encourage the cellular machinery to completely ignore mutated gene.
In the Duchenne Muscular Dystrophy research scientists are trying to change the DMD gene mutation into mutation that causes much milder disease known as Becker's Muscular Dystrophy. Here some amount of dystrophin is produced in the body, unlike Duchenne Muscular Dystrophy.
To achive this scientists constructed antisense oligonucleotides. These oligonucleotides are 20-30 nucleotides long single-stranded RNA molecules. These are designed such that they specifically bind to an exon that contains the mutated part of the gene or DNA. As a result mutation which is present in the exon is hidden from cellular machinery involved in protein production. Therefore the mutated part of exon is not transcribed into messenger RNA molecule, as a result smaller protein is produced in the body. This technique reduces the severity of Duchenne Muscular Dystrophy.
Even though the exon-skipping gene therapy is not yet tried in humans, however this technique was successfully worked in mice and also in dogs. It will take some time to do clinical trials on humans, as more animal research are being conducted on this field and technique.
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