Biotechnology and its Applications — BIOLOGY STD 12 Science — Question

Adenosine Deaminase (ADA) deficiency by M Blease and WF Andresco of National Institute of Health. This particular enzyme is crucial for the immune system to function. 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 and in, others by enzyme replacement therapy. But, the problem with both of these approaches is that they are not completely curative.
Steps followed in enzyme replacement gene therapy are given below:

1. In first step of gene therapy, lymphocytes from the blood of the patient are grown in a culture outside the body.
2. A functional ADA cDNA (using a retroviral vector) is then introduced into these lymphocytes which are subsequently returned to the patient.
3. As these cells are not immortal, the Patient requires periodic infusion of such genetically engineered lymphocytes. But if the gene isolated fiom marrow cells producing ADA is introduced into cells at early embryonic stages, it could be a permanent cure.