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Gene Therapy and Its types


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What is Gene Therapy ?
  •  Gene therapy is the technique of genetic engineering to replace ' a faulty gene ' by a normal healthy functional gene.
Types of Gene Therapy
  • It is of two types
  • Germline Gene Therapy.
  • In this type of gene therapy germ cells, i.e. , sperms or eggs (even zygotes) are modified by the introduction of functional genes, which are ordinarily integrated into their genomes.
  • Somatic Cell Gene Therapy
  • In this type of gene therapy, the gene is introduced only in somatic cells.
  • Only introduction of a new gene into the somatic cells is allowed at present.
  • Genetic modification in the germ cells of the offspring is not permissible.
Diseases and Gene Therapy
  • The diseases for which scientists are making serious attempts to control through gene therapy are severe combined immunodeficiency (SCID) disease, Duchenne muscular dystrophy and cystic fibrosis.
  • These disorders are mainly due to single gene defects. Cancer , cardiovascular diseases, diabetes, hypertension, arthritis. sickle cell anaemia , etc. are complex genetic disorders.
  • However, the day is not far off when these diseases can be cured through gene therapy.

Example . Adenosine Deaminase ( ADA ) Deficiency
  • The first clinical gene therapy was given in 1990 to a 4 - year old girl with adenosine deaminase ( ADA ) deficiency.
  • This enzyme is very important for the immune system to function.
  • ADA deficiency can lead to severe combined immune deficiency (SCID) .
  • SCID is caused due to defect in the gene for the enzyme adenosine deaminase.
  • In some children ADA deficiency can be cured by bone marrow transplantation.
  • However, in others it can be treated by enzyme replacement therapy in which functional ADA is given to the patient by injection.
  • But in both approaches the patients are not completely cured.
  • Because these patients do not have functional T - lymphocytes, they cannot provide immune responses against invading pathogens.
  • As a first step towards gene therapy, lymphocytes , a kind of white blood cells , are extracted from the bone marrow of the patient and are grown in a culture outside the body.
  • A functional ADA cDNA (using a retroviral vector) is then introduced into these lymphocytes, which are reinjected to the patient's bone marrow.
  • But as these cells do not always remain alive, the patient requires periodic infusion of such genetically engineered lymphocytes.
  • However, if the isolated gene from bone marrow cells producing ADA is introduced into cells at early embryonic stages, it can be a permanent cure.


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