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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