Gene Therapy - ADA Deficiency Treatment MCQ - Practice Questions with Answers

• If a person is born with a hereditary disease, can a corrective therapy be taken for such a disease? Gene therapy is an attempt to do this.
• Gene therapy is the technique of genetic engineering to replace ‘a faulty gene’ by a normal healthy functional gene.
• Correction of a genetic defect involves the delivery of a normal gene into the individual or embryo to take over the function of and compensate for the non-functional gene.
• There are two types of gene therapy:
  • Germline gene therapy: The germ cells, that is, sperm, ova, and zygote are modified by the introduction of functional genes.
  • Somatic cell gene therapy: The functional gene is introduced only in the somatic cells.

ADA Deficiency:

• The first clinical gene therapy was given in 1990 to a 4-year old girl with adenosine deaminase (ADA) deficiency.
• Adenosine deaminase deficiency is one form of SCID (severe combined immunodeficiency) disorder. 
• The disease is caused due to a mutation in the adenosine deaminase gene on chromosome 20.
• This enzyme is crucial for the immune system to function.
• There are no functional T-cells in the patients. 
• In some children, ADA deficiency can be cured by bone marrow transplantation
• In others, it can be treated by enzyme replacement therapy, in which functional ADA is given to the patient by injection.
• But the problem with both of these approaches is that they are not completely curative. 
• As a first step towards gene therapy, lymphocytes from the blood of the patient are grown in a culture outside the body. 
• A functional ADA cDNA (using a retroviral vector) is then introduced into these lymphocytes, which are subsequently returned to the patient. 
• However, as these cells are not immortal, the patient requires a periodic infusion of such genetically engineered lymphocytes. 
• However, if the gene isolate from marrow cells producing ADA is introduced into a cell at early embryonic stages, it could be a permanent cure.