What is gene therapy ? IIIustrate using the example of adenosine deaminase (ADA) deficiency.

Explanation

Gene therapy is a collection of methods that allows Correction of a gene defect that has been diagnosed in a child/embryo. Here genes are inserted into a person.s cells and tissues to treat a disease. Correction of a genetic defect involves delivery of a normal gene into the individual or embryo to take ove the fuction of and compensate for the non-functional gene.
Adenosine deaminase (ADA) enzyme is curcial for the immune system to fuction. The disorder is caused due to the deletion of the gene for adenosine deaminase. 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 fuctional ADA cDNA (using a retroviral vector is then introduced into these lymphocytes, which are subsequently returned to the patient.