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Gene therapy is defined as the specific genetic manipulation and modification of an organism’s genome or genes through the delivery of therapeutic DNA or genes into host cells with little or no toxicity as a way of treating an inherited genetic disease or correcting a disorderly gene. Gene therapy techniques are basically used to correct the genetic defects of somatic cells i.e. cells of the body that do not in any way contribute to hereditary (the transfer of genetic information from parents to their offspring via the genes). It is a promising field of clinical research that is still an experimental discipline but it has the potential to revolutionize medicine in terms of the way genetic disorders are managed. Gene therapy uses therapeutic DNA to repair defective gene copy in genetic disorder patients. In gene therapy techniques, mutant genes of a cell are replaced with normal or wild type gene that carries therapeutic proteins or DNA expected to treat a particular acquired genetic disease such as cancer and severe combined immune deficiency (SCID) disease in the affected human host. Faulty genes in people with genetic disorder or disease can be replaced with functional genes through a series of molecular/genetic engineering techniques in which the nucleic acid molecules are specifically modified to correct the anomaly. Gene therapy techniques as shall be seen later in this section are usually carried out in two main approaches.

  • In vivo gene therapy: In in vivo gene therapy, therapeutic DNA is transferred directly into the body of the host using gene delivery vectors or techniques. This method or technique of gene therapy is generally known as the direct delivery technique.
  • Ex vivo gene therapy: In ex vivo gene therapy, some defective genes or cells are extracted from the body and treated in vitro, selected and thentransferred back into the body. This method is known as the cell-based delivery technique.

Therapeutic DNA or protein is to gene therapy what antibiotics are to conventional medicine. Instead of using the traditional antimicrobial agents such as antibiotics and chemotherapy known to medicine for treating some diseases, gene therapy employs “functional genes” as its medicine to treat defects in the gene of an organism. With therapeutic DNA, cellular dysfunction or genetic disease in a cell can be corrected by inserting functioning genes into the cell. As the genetic disorder is being corrected by the functional gene, a normal or new cellular function is restored in the affected individual.

Genetic disorder is a disease that is caused by a mutation (i.e. a change) in the gene of an organism. Such molecular diseases can be passed on from parent to their offspring who inherit the defective gene. They usually arise when the genes or genetic compositions of an organism are altered so that the proteins they encode are incompetent to carry out their normal physiological function in the cell. In order words, such defective genes begin to express itself in an abnormal way that affects the organism’s phenotype. The completion of the “human genome project” is a landmark for advancing gene therapy applications in clinical medicine. This is because the practice will help to identify the genes responsible for a wide variety of human diseases with a view to correcting and treating them effectively. Information from the human genome project will help molecular biology scientists to compare the genetic makeup of normal and unhealthy individuals with a view to deciphering whether or not mutation in the gene of an organism could be responsible for some genetic disorders. This can be improved upon by the techniques of gene therapy via targeted delivery of normal and therapeutic genes or DNA to treat genetic disorders.

The fact that we carry two (2) copies of practically all genes (with each derived from our mother and father) may be answerable to the question why most people (with defective genes) do not suffer any significant genetic disease. It is possible that virtually every human being on earth harbour one defective gene or the other. But these abnormal genes are apparent in some individuals (who show clinical signs of genetic disorders) and obscure or unapparent in others who are unaware of any defective gene in them. 

Further reading

Cooper G.M and Hausman R.E (2004). The cell: A Molecular Approach. Third edition. ASM Press.

Das H.K (2010). Textbook of Biotechnology. Fourth edition. Wiley edition. Wiley India Pvt, Ltd, New Delhi, India.

Davis J.M (2002). Basic Cell Culture, A Practical Approach. Oxford University Press, Oxford, UK. 

Mather J and Barnes D (1998). Animal cell culture methods, Methods in cell biology. 2rd eds, Academic press, San Diego.

Noguchi P (2003).  Risks and benefits of gene therapy.  N  Engl J Med, 348:193-194.

Sambrook, J., Russell, D.W. (2001). Molecular Cloning: a Laboratory Manual, 3rd edn. Cold Spring Harbor Laboratory Press, New York.

Tamarin Robert H (2002). Principles of Genetics. Seventh edition. Tata McGraw-Hill Publishing Co Ltd, Delhi.     

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