Gene therapy involves inserting copies of a normal allele into the chromosomes of an individual who carries a faulty allele. If a mutated gene causes a necessary protein to be faulty or missing, gene therapy may be able to introduce a normal copy of the gene to restore the function of the protein.
However, it is not always successful, and research is continuing.
It is illegal to do this to sex cells (Germ Line Therapy), because any (bad) changes would be inherited by the individual’s offspring. Instead, gene therapy is used on somatic (body) cells. This means that the individual could pass on their faulty allele to their children, even if they get better themselves L
A gene that is inserted directly into a cell usually does not function. Instead, a carrier called a vector is genetically engineered to deliver the gene. Certain viruses are often used as vectors because they can deliver the new gene by infecting the cell. The viruses are modified so they can’t cause disease when used in people. If the treatment is successful, the new gene delivered by the vector will make a functioning protein.
The basic process
- Doing research to find the gene involved in the genetic disorder.
- Cutting out the normal allele. Special enzymes are used to do this.
- Making many copies of the allele.
- Insert copies of the normal allele into the target cells of a person who has the genetic disorder, via liposome’s / plasmids or GM virus
- The normal gene is transcribed and translated
- A functioning protein is produced.
Researchers are testing several approaches to gene therapy, including:
- Replacing a mutated gene that causes disease with a healthy copy of the gene = currently being tested
- Inactivating, or “knocking out,” a mutated gene that is functioning improperly.
- Introducing a new gene into the body to help fight a disease.
Problems in the process
- the alleles may not go into every target cell
- the alleles may join with the chromosomes in random places, so they do not work properly
- treated cells may be replaced naturally by the patient’s own untreated cells
Plasmid = extra loop of DNA that has been GM to contain the “correct” allele to produce the functioning protein
Liposome = spherical phospholipid bilayer that fuses with the cell membrane, whilst carrying in the GM plasmid
- The normal allele is cut out via restriction enzymes
- It is inserted into the plasmid via ligase – the plasmid has been genetically modified
- The (-ve)plasmid combines with the (+ve) liposome (the liposome on the outside) = Plasmid – liposome complex formed
- Liposome fuses with the cell membrane when carrying the plasmid into the cell
- The plasmid enters the nucleus, and the normal gene is inserted into the DNA and replaces the faulty gene
- The mRNA transcribes the correct sequence
- This sequence is translated by ribosome’s in the cytoplasm to create a functioning protein that can open the CFTR channel
PROS & CONS of Gene Therapy
- There is only one way of curing the disease – replacing the defective gene with a healthy copy – and therefore gene therapy is the only hope of finding cures for such disorders
- If gene therapy targets the reproductive cells of carriers of such genetic disorders as cystic fibrosis, Parkinson’s disease, or cancer, it is possible that any children the carrier goes on to have would be free of the defective gene and on a bigger scale the disease can be wiped out completely
- Gene therapy, when successful, can have a number of advantages over drug therapy such as providing a cure rather than easing the symptoms.
- Comprehensive federal laws, regulations, and guidelines help protect people who participate in research studies (called clinical trials).
- The current lack of knowledge and understanding of the treatment means that its safety is unknown. The current scientific understanding is based on theory rather than solid fact. This, however, can be improved with further research and practice.
- In clinical trials already carried out the effects of the treatment have only been short-lived. To achieve long term results much more research is needed.
- Drug therapy, although not offering the possibility of a cure, is a tried and tested method and is therefore deemed safer
- With current knowledge there is no guarantee that the vector carrying the healthy gene will end up in the specific place it is intended – there is a risk of causing even more damage to the genetic make-up that can result in severe consequences for the patient
- Very serious side effects e.g. inflammatory response, headaches, fatigue, fever, increased heart rate
Ethical, religious and moral issues:
The intrusive nature of gene therapy means that we can discover information about our genetic make-up than we are meant to know. The knowledge could have a negative impact on their lives and if that knowledge was to influence any life decisions in a negative way then it is questionable whether genetic screening is morally correct.
Genetic screening can also be carried out on unborn babies – if this screening showed that a child was carrying a disease this may lead to the parents deciding to abort the child. This is clearly a very morally questionable act as many would argue that a person does not have the right to play God with another person’s life.
Similarly, a couple who are aware of their genetic make-up and know that they’re both carriers of a specific genetic disorder may decide against having children to avoid passing on the defective gene. Again, many would argue that this goes against the natural order.
Gene therapy has the potential to be misused – for instance the concept of “designer babies”, where specific genes are selected in order to create the perfect child.
So, the cons of gene therapy in terms of quantity very clearly outweigh the pros.