People who are born with a genetic disease are treated through gene therapy. Through gene therapy, the faulty gene is replaced with a normal and healthy gene. Through the technique of genetic engineering, the genetically defective genes are isolated from the newborn or unborn child, a recombinant gene is produced and then transferred in its place. In this method, that part of the DNA (which contains the culprit gene) is cut out and the correct piece is added in its place. With this method, fatal diseases like cystic fibrosis, sickle cell anaemia, severe combined immunodeficiency are treated. Gene therapy has the following steps: (i) Identifying the gene causing the genetic disease. (ii) To find out the role of the product of this gene in disease/health. (iii) Isolation and cloning of genes. (iv) Development of suitable methods of gene therapy.
Gene therapy was first used in 1990 to overcome adenosine deaminase (ADA) deficiency in a four-year-old girl. This enzyme is essential for the functioning of the immune system. This problem occurs due to the absence of the enzyme adenosine deaminase. In some children, ADA deficiency is treated with a bone marrow transplant. While in others treatment is by enzyme replacement therapy, in this, active ADA is given to the patient through a injection. The drawback of both the above methods is that they are not completely curative. In gene therapy, first of all lymphocytes are extracted from the patient's blood and cultured outside the body. The cDNA of activated ADA is introduced into the lymphocyte (using a retroviral vector) and finally returned to the patient's body. These cells are dead. Therefore, genetically engineered lymphocytes need to be isolated from the patient's body from time to time. If good genes isolated from marrow cells are introduced into early embryonic cells, this could lead to a permanent treatment.