Sunday, 1 April 2012


Gene Therapy
How do you make a patient with a potentially fatal illness better? Why, inject them with viruses, of course. Now, while this notion may seem somewhat contradictory - after all, aren’t viruses supposed to do more damage than good? -  it is in fact a scientific breakthrough which could change the way medicine is practised and save countless lives.

Figure 1: Repaired DNA Sequence (Nienhuis, 2008)

Gene therapy is a rapidly developing area of genetic science with the potential to provide efficient and effective medical treatments for hundreds of diseases. It involves the replacement of malfunctioning genes within a patient’s cells with a new set of correctly functioning genes, in order to treat such diverse medical conditions as Parkinson’s disease, sickle-cell anaemia and haemophilia (Nienhuis, 2008).

 This replacement of the patient’s faulty genes can be achieved via two different techniques: in-the-body gene therapy and out-of-the-body gene therapy; both of which involve the use of viral vectors in order to “carry the genetic cargo into [the host] cells” (Nienhuis, 2008).

In-the-body gene therapy often involves the direct injection of the viral vector into the region of the patient’s body that contains the malfunctioning cells and relies on “the natural tendency of viruses to infect certain organs,” (Nienhuis, 2008). Researchers typically use adeno-associated viruses in gene therapy – in place of the adenoviruses that were once used – as they are non-pathogenic and, unlike adenoviruses, do not trigger a hostile response from the patient’s immune system. (Gene Therapy Net, 2012) These viruses are especially useful in the treatment of diseases such as haemophilia because, once they have entered the bloodstream, they naturally target the liver – where blood clotting factors are added to the blood.

 However, as adeno-associated viruses lack the necessary genes required to propagate on their own (they are reliant on adenoviruses in nature), innocuous adenovirus DNA must be added to them in order that this method of treatment be viable (Nienhuis, 2008).

In the other major type of gene therapy, out-of-the-body gene therapy, a patient’s blood or bone marrow is removed from their body and the replacement genes are transplanted into the immature cells, which are then injected back into the patient’s bloodstream. The malfunctioning cells are then gradually replaced as the treated cells multiply in the patient’s body.


Figure 2 : Adeno-associated Viral Vector 
 This method is currently being trialled for use in the treatment of severe combined immuno-deficiency (SCID) – a fatal disease which results in little or no immune response in the patient. However, the researchers’ use of retroviruses (an RNA virus which uses the enzyme reverse transcriptase to transcribe its RNA to DNA inside the host cell (MedicineNet, 2011)) caused genetic mutations –such as leukemia - in the 5 out of the 30 patients that underwent the trial therapy. This potentially fatal side-effect is a serious drawback to this otherwise effective use of gene therapy in the treatment of SCIDS and is due to the tendency of retroviruses to disrupt other functioning genes by “stitch[ing] their gene anywhere into [the patient’s] DNA,” (Nienhuis, 2008).

 While there are still many flaws to ironed out, the use of gene therapy is a marked advance in the use of genetics in medical practice and it has shown promising results in trial treatments of a wide-array of diseases. It is a technology that is still very much in its developmental phase and, therefore, current inadequacies aside, the potential benefits of this type of treatment could be far beyond the scope of current researchers’ understanding and imagination.

Bibliography

Basu, S., 1998. The Adenovirus Family. [Online]
Available at: http://virus.stanford.edu/adeno/adeno.html
[Accessed 17 March 2012].
Gene Therapy Net, 2012. Gene Therapy Net.com. [Online]
Available at: http://www.genetherapynet.com/viral-vectors/adeno-associated-viruses.html
[Accessed 17 March 2012].
MedicineNet, 2011. Definition of Retrovirus. [Online]
Available at: http://www.medterms.com/script/main/art.asp?articlekey=5344
[Accessed 16 March 2012].
Nienhuis, A., 2008. How Does Gene Therapy Work?. [Online]
Available at: http://www.scientificamerican.com/article.cfm?id=experts-gene-therapy
[Accessed 11 March 2012].

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