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Gene Therapy One Of Applications Of Genetic Engineering

INTRODUCTION

Gene therapy is one of the applications of the genetic engineering. It is a technique which correcting defective gene that is responsible for disease development (cited Safdar, 2010). Gene therapy also involves the addition of healthy and functional copy of the faulty gene into the target cells of the body. Gene therapy generally works by inserting a normal gene into the genome to replace an abnormal gene in the target cells. There are two types of gene therapy. Firstly, germ line gene therapy which involves modification of genetic material in the gamete cells that would be heritable and can be pass through to the next generation. Secondly, somatic gene therapy which involves insertion of therapeutic gene into somatic cells of the patient that only effect to the individual patient only and will not be inherited by patient’s offspring.( cited in Ten Tailed Fox, 2009).

Various genetic disorder diseases commonly are caused by faulty genes. With gene therapy, instead of treating the symptoms of the disease, treatment also target and correct the underlying cause of disease and eventually improve the faulty genes to normal genes. One of the genetic diseases that apply gene therapy as alternative treatment is Cystic Fibrosis.

Cystic Fibrosis (CF) is one of the most well-known hereditary lethal diseases. A study conducted by UK Cystic fibrosis Gene Therapy Consortium (UK CFGTC) stated that approximately, 50 000 people and 1 in 2500 newborns around the world are affected. CF is an autosomal recessive disorder which caused by the mutation of Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) protein that leads to abnormally thick secretion of mucus. The organs most affected by CF are the lungs, gut, pancreases, liver and reproductive tract, but lung infection is the most serious affected by CF. (cited in Metharom, 1997). Continuous inflammation, damaged lungs and respiratory failure are results of repeated cycles of infection that may leads to death.

With the development of effective treatment to overcome CF, gene therapy was introduced by scientist in 1990 which promises new opportunity for CF patients to have a better and long life span. This gene therapy involves replacing the detective CFTR gene with the normal one in the affected cells. As the results, the functional CFTR are being produced in all target cells and the CFTR gene will then conducts the production of normal CFTR protein which acts as a medium that allows releasing chloride and other ions. But this is opposite with people who have CF, where CFTR protein is detective and the cells do not discharge chloride ions.

Although, gene therapy has the capability in treating CF, it still faces with various issues. This report consists of history of CF gene therapy and genetic techniques of gene therapy on CF. Research findings also include the advantages and disadvantages of using gene therapy in treating CF.

2.0 BACKGROUND GENETIC

Gene therapy has shows that much positive feedback in treating genetic diseases although there are many failures happened. Gene therapy for CF first discovered in 1990 when scientist treated defective CFTR successfully and they added the normal copies of the gene to laboratory cell structures. The first experimental CF gene therapy treatment was given to CF’s patient in 1993 (cited in Schoenstadt, 2009). The table below shows the major events that occurred due to development of gene therapy in treating Cystic Fibrosis.

YEARS

MAJOR EVENTS

1936

The previously nameless condition was referred as “cystic fibrosis with bronchiectasis” by Fancon

1938

The first comprehensive description of cystic fibrosis symptoms was developed by Anderson of Columbia University.

1949

The cystic fibrosis was established as a recessive genetic disorder.

1953

Sant’Agnes of Columbia University reported that CF patients secrete excessive amounts of salt in their sweat. This results in development of the sweat test as a diagnosis standard for cystic fibrosis.

1961

The first CF care centers was established by the CF Foundation

Early 1980’s

The organ damage caused by CF was associated by researches with a malfunction of the epithelial tissues.

1989

A team led by Tsui and Riordan of the hospital for Sick Children in Toronton discovered the gene responsible for CF and named it as CFTR.

The gene is mapped to chromosome 7q.

1990

CF researchers achieved test tube “proof of concept” for gene therapy.

1993

First gene therapy tested in person with CF and it showed that gene therapy corrects CF cells in nasal passages.

1995

A drop of fats has been successfully used to carry the working copy of a crucial gene into the nose lining of patients with CF.

1999

A study report in The Lancet showed that gene therapy can improve at least one of the underlying abnormalities in CF, a diseases that can causes chronic lung diseases.

2001

University of Iowa researchers have used new gene therapy technique to correct the common CF genetic defect in CFTR.

2006

Cystic Fibrosis Foundation Therapeutics-supported studies in Australia and UNC showed that hypertonic saline helps clear CF mucus and becomes a therapeutic option.

The first compound for CF, discovered through high-throughput screening at Vertex Pharmaceuticals, begins clinical trials.

2007

New researches have suggested that a modified version of the virus that can cause AIDS could become the basis of a prenatal gene therapy for CF

SOURCE: http://runsickboyrun.blogspot.com/2009/08/cystic-fibrosis-history-and-timeline.html.

3.0 GENETIC TECHNIQUES

In gene therapies, there are three main techniques that are being used in treating diseases. The first is Gene addition, in which the genetic material is added to the target cells with no attempt to incorporate it into chromosomes. Second one is techniques of gene repair that replace abnormal segments of DNA in defective genes in their normal chromosomal site. The last one is Gene replacement techniques which allow deletion of the abnormal gene from its chromosome and replacement with a normal gene. (cited in Sade RM, Khushf G., 1998).

In order to treat CF, the common technique used is Gene replacement by using vector. Vector is a DNA molecule (virus) act as a medium to transfer foreign genetic material into another cell. Instead of introducing new genetic material into target cells vectors are also agents to which new genetic material is attached. Diagram below shows the working of a virus acts a vector in gene therapy.

http://vectorblog.org/wp-content/uploads/2011/01/gene-1.jpg

FIGURE 1: The working of a virus acts a vector in gene therapy.

SOURCE: http://vectorblog.org/science-and-innovation-top-10-for-2010/?isalt=0

In treating CF disease, the virus that is being used in this gene therapy is Adeno Associated Virus. The flowchart below shows the mechanism of using gene therapy in treating CF.

SOURCE: http://chestjournal.chestpubs.org/content/120/3_suppl/124S.full.

http://chestjournal.chestpubs.org/content/121/3_suppl/98S.full.html.

First step to do is designing a vector by modifying the gene of the virus. We need to remove the rep gene which codes for proteins that responsible for viral replication as well as cap gene, which codes for capsid structural proteins. Then, we insert the normal CFTR gene in the virus. Second step is producing the virus. After inserting the CFTR gene in the virus, we transfer the vector into a 'packaging' cell line so that the vector will combine with protein needed to assemble the virus. Next, we collect the virus sample from the growth medium and add into the Petri dish containing the CF cells. The virus give effect to the cell as it integrates the DNA into specific location on chromosome 19. Last step, we transfer the vector into CF patient. CFTR gene in the cell will transcribe into mRNA and this induces the cell to produce normal CFTR protein in the target cells. Diagram below show the mechanism of vector in treating Cystic Fibrosis.

http://ghr.nlm.nih.gov/handbook/illustrations/therapyvector.jpg

FIGURE 2: The mechanism of vector in treating Cystic Fibrosis

SOURCE: http://ghr.nlm.nih.gov/handbook/illustrations/therapyvector.jpg

4.0 SOCIAL ISSUES

In recent years, many types of techniques have been developed to identify genes associated

with specific diseases. Society always debate over the ethics of using gene technology to treat human beings when recombinant DNA research began. Tables below show advantages, disadvantages, ethical and social of practicing gene therapy to treat genetic diseases such as Cystic Fibrosis.

ADVANTAGES OF GENE THERAPY

Gene therapy promotes in providing better and normal life for those who practise the therapy. (Ten Tailed Fox, 2009).

The practice of gene therapy on CF patients can solve their problems by replacing none functional gene with functional one. (cited in S. Muniba, 2010)

Gene therapy has high success rate compared to other methods in treating CF disease.

Gene therapy helps patients to avoid from practicing unnecessary treatment and alternative which may be dangerous to them.

SOURCE: http://www.biotecharticles.com/Genetics-Article/Gene-Therapy-Advantages-and- Disadvantages-271.html

DISADVANTAGES OF GENE THERAPY

Scientist stated that correcting the defect in people who had diseases is much harder

than achieving correction in cells in the laboratory .It means that there are also numbers of trial that results in failure. (cited in Healingwell.com )

Practice of gene therapy using vector may induce immune response in the patients. The gene that is injected or sprayed into patient’s target cells may trigger antibodies to kill the vectors. ( cited in William, 2000).This is because virus is used as a vector to transport the therapeutic gene.

The use of gene therapy in treating CF will cause in diminishing the gene pool. Their patient’ s next generation will have to survive with the changes in their genomes.(cited in Sade RM, Khushf G., 1998 ).

Chance of inducing a tumor .If the DNA is integrated in the wrong place in the genome, for example in a tumor suppressor gene, it could induce a tumor. (cited in Healingwell.com)

SOURCE: http://academicdepartments.musc.edu/humanvalues/pdf/gene-therapy.pdf

In conclusion, gene therapy is a best solution in treating cystic fibrosis because it has the high chances to eliminate this genetic disorder disease. Muniba stated that gene therapy could be last cure for every genetic disease. People who take gene therapy will make up their mind if they also face with this problem because this type of treatment can be the last hope for them in treating hereditary disease like Cystic Fibrosis.Government should concerns regarding the harms that may be associated with gene therapy and the beneficial uses of gene technology are required.

(1547 words)


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