Gene Therapy is a emerging technology helping to manipulate the defective genes, Basic understanding of the principles will enlighten the younger generation of medical professionals
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Genes, which are carried on chromosomes, are the basic physical and functional units of heredity. Genes are specific sequences of bases that encode instructions on how to make proteins. it’s the proteins that perform most life functions and even make up the majority of cellular structures.
Each of us carries about half a dozen defective genes. We remain blissfully unaware of this fact unless we, or one of our close relatives, are amongst the many millions who suffer from a genetic disease. About one in ten people has, or will develop at some later stage, an inherited genetic disorder, and approximately 2,800 specific conditions are known to be caused by defects (mutations) in just one of the patient's genes.
Most of us do not suffer any harmful effects from our defective genes because we carry two copies of nearly all genes, one derived from our mother and the other from our father. The only exceptions to this rule are the genes found on the male sex chromosomes. Males have one X and one Y chromosome, the former from the mother and the latter from the father, so each cell has only one copy of the genes on these chromosomes
In the majority of cases, one normal gene is sufficient to avoid all the symptoms of disease. If the potentially harmful gene is recessive, then its normal counterpart will carry out all the tasks assigned to both. Only if we inherit from our parents two copies of the same recessive gene will a disease develop.
Gene therapy is the insertion of genes into an individual's cells and tissues to treat a disease, such as a hereditary disease in which a deleterious mutant allele is replaced with a functional one. Although the technology is still in its infancy, it has been used with some success.
Advances in understanding and manipulating genes have set the stage for scientists to alter a person's genetic material to fight or prevent disease. Gene therapy is an experimental treatment that involves introducing genetic material (DNA or RNA) into a person's cells to fight disease.
Gene therapy is ‘the use of genes as medicine’. It involves the transfer of a therapeutic or working gene copy into specific cells of an individual in order to repair a faulty gene copy. Thus it maybe used to replace a faulty gene, or to introduce a new gene whose function is to cure or to favourably modify the clinical course of a condition.
Today, gene therapy is the ultimate method of protein delivery, in which the delivered gene enters the body's cells and turns them into small "factories" that produce a therapeutic protein for a specific disease over a prolonged period.
Antisense therapy is a form of treatment for genetic disorders or infections. When the genetic sequence of a particular gene is known to be causative of a particular disease, it is possible to synthesize a strand of nucleic acid (DNA, RNA or a chemical analogue) that will bind to the messenger RNA (mRNA) produced by that gene and inactivate it, effectively turning that gene "off".
On September 14, 1990 at the U.S. National Institutes of Health, W. French Anderson M.D. and his colleagues R. Michael Blaese, M.D., C. Bouzaid, M.D., and Kenneth Culver, M.D., performed the first approved gene therapy procedure on four-year old Ashanthi DeSilva. Born with a rare genetic disease called severe combined immunodeficiency (SCID),
In Ashanthi's gene therapy procedure, doctors removed white blood cells from the child's body, let the cells grow in the laboratory, inserted the missing gene into the cells, and then infused the genetically modified blood cells back into the patient's bloodstream.
As of early 2007, she was still in good health, and she was attending college. Some would state that the study is of great importance despite its indefinite results, if only because it demonstrated that gene therapy could be practically attempted without adverse consequences.
Viral vectors are a tool commonly used by molecular biologists to deliver genetic material into cells. This process can be performed inside a living organism (in vivo) or in cell culture (in vitro). Viruses have evolved specialized molecular mechanisms to efficiently transport their genomes inside the cells they infect.
Gene that is inserted directly into a cell usually does not function. Instead, a carrier called a vector is used to introduce the therapeutic gene into the patient's target cells. The most common vector that is used is a virus that has been genetically altered to carry normal human DNA. Viruses cause diseases in humans by encapsulating and delivering the genes into cells.
Gene therapy can target somatic (body) or germ (egg and sperm) cells. In somatic gene therapy the recipient's genome is changed, but the change is not passed on to the next generation; whereas with germ line gene therapy the newly introduced gene is passed on to the offspring.
Low toxicity: The viral vector should have a minimal effect on the physiology of the cell it infects.
Stability: Some viruses are genetically unstable and can rapidly rearrange their genomes. This is detrimental to predictability and reproducibility of the work conducted using a viral vector and is avoided in their design.
Lentivirus (lenti-, Latin for "slow") is a genus of slow viruses of the Retroviridae family, characterized by a long incubation period. Lentiviruses can deliver a significant amount of genetic information into the DNA of the host cell, so they are one of the most efficient methods of a gene delivery vector. HIV, SIV, and FIV are all examples of lentiviruses.
Retroviruses can infect only dividing cells. The viral genome in the form of RNA is reverse-transcribed when the virus enters the cell to produce DNA, which is then inserted into the genome at a random position by the viral integrase enzyme
Their primary applications are in gene therapy and vaccination. Since humans commonly come in contact with adenoviruses, which cause respiratory, gastrointestinal and eye infections, they trigger a rapid immune response with potentially dangerous consequences To overcome this problem scientists are currently investigating adenoviruses to which humans do not have immunity.
Adeno-associated virus (AAV) is a small virus which infects humans and some other primate species. AAV is not currently known to cause disease and consequently the virus causes a very mild immune response. AAV can infect both dividing and non-dividing cells and may incorporate its genome into that of the host cell. These features make AAV a very attractive candidate for creating viral vectors for gene therapy
The simplest method is the direct introduction of therapeutic DNA into target cells. This approach is limited in its application because it can be used only with certain tissues and requires large amounts of DNA.
Nonviral approach involves the creation of an artificial lipid sphere with an aqueous core. This liposome, which carries the therapeutic DNA, is capable of passing the DNA through the target cell's membrane
DNA/lipid complexes are easy to prepare and there is no limit to the size of genes that can be delivered. Because carrier systems lack proteins, they may evoke much less immunogenic responses. More importantly, the cationic lipid systems have much less risk of generating the infectious form or inducing tumorigenic mutations because genes delivered have low integration frequency and cannot replicate or recombine.
Nonviral substances such as Ormosil have been used as DNA vectors and can deliver DNA loads to specifically targeted cells in living animals. (Ormosil stands for organically modified silica or silicate)
Transfection is the process of introducing nucleic acids into cells by non-viral methods. The term "transformation" is preferred to describe non-viral DNA transfer in bacteria and non-animal eukaryotic cells; "transduction" is often used to describe virus-mediated DNA transfer.
The germ line of a mature or developing individual is the line (sequence) of germ cells that have genetic material that may be passed to a child
Germ line cells are immortal, in the sense that they can reproduce indefinitely. This is largely due to the activity of the enzyme known as telomerase. This enzyme extends the telomeres of the chromosome, preventing chromosome fusions and other negative effects of shortened telomeres.
It would be a large vector capable of carrying substantial amounts of genetic code, and scientists anticipate that, because of its construction and autonomy, the body's immune systems would not attack it. A problem with this potential method is the difficulty in delivering such a large molecule to the nucleus of a target cells.
In the study, immune cells were removed from the patients' bodies, modified with a disabled AIDS virus known as a lentivirus, and then intravenously returned. The genetically altered cells disseminated anti-HIV material and prevented HIV from reproducing( 07 November, 2006)
Gene delivery: Successful gene delivery is not easy or predictable, even in single-gene disorders. For example, although the genetic basis of cystic fibrosis is well known, the presence of mucus in the lungs makes it physically difficult to deliver genes to the target lung cells. Delivery of genes for cancer therapy may also be complicated by the disease being present at several sites. Gene-therapy trials for X-linked severe combined immunodeficiency (X-SCID), however, have been more successful
Current uses of gene therapy focus on treating or curing existing conditions. In the future, the focus could shift to prevention. As more of the human genome is understood, medicine will know more about which genes contribute to or cause disease. With that knowledge in hand, gene therapy could be used to head off problems before they occur.
Gene mutations probably play a role in many of today's most common diseases, such as heart disease, diabetes, immune system disorders, and birth defects. These diseases are believed to result from complex interactions between genes and environmental factors. When genes for diseases have been identified, scientists can study how specific environmental factors, such as food, drugs, or pollutants interact with those genes.
Over the last 20 years, the initial thoughts of gene therapy have been transformed into reality with more than 175 clinical trials and 2,000 patients already treated . Yet with all the trials, there is still no conclusive evidence for efficacy.
The most likely candidates for future gene therapy trials will be rare diseases such as Lesch-Nyhan syndrome, a distressing disease in which the patients are unable to manufacture a particular enzyme. This leads to a bizarre impulse for self-mutilation, including very severe biting of the lips and fingers. The normal version of the defective gene in this disease has now been cloned.
LNS is transmitted as and X-linked recessive trait. Female carriers do not show the symptoms. LNS is characterized by self-mutilating behaviours such as lip and finger biting and/or head banging. The deficiency of HPRT activity leads to accumulation of phosphoribosylpyrophosphate.
Neurologix a biotech company announced that they have successfully completed its landmark Phase I trial of gene therapy for Parkinson's Disease.
This was a 12 patient study with four patients in each of three dose escalating cohorts. All procedures were performed under local anesthesia and all 12 patients were discharged from the hospital within 48 hours of the procedure, and followed for 12 months. Primary outcomes of the study design, safety and tolerability, were successfully met. There were no adverse events reported relating to the treatment.
Viruses can infect more than one type of cells. Viral vectors may alter more than the intended cells. Or the new gene might be inserted into the wrong location in the DNA, causing cancer or other damage.
When DNA is injected directly into a tumor there is a chance that some DNA could be introduced into germ cells, producing inheritable changes.
The gene might be over-expressed (toxicity); the viral vector could cause inflammation or immune reaction; the virus could be transmitted to other individuals or the environment.
Gene therapy to alleviate pain could appear surprising and perhaps not appropriate when opioids and other active molecules are available. However, the possibility of introducing a therapeutic protein into some targeted structures, where it would be continuously synthesised and exert its biological effect in the near vicinity of, or inside the cells, might avoid some drawbacks of "classical" drugs.
Numerous other molecules involved in pain processing or associated with chronic pain have been identified and the gene-based techniques might be particularly adapted for the evaluation of the possible therapeutic interest of these new potential targets