Read the following statements about the treatment of adenosine deaminase (ADA) deficiency:
A. The enzyme adenosine deaminase is crucial for the immune system to function.
B. In enzyme replacement therapy, functional ADA is given to the patient by injection.
C. A functional ADA cDNA is introduced into the patient’s cultured lymphocytes using a bacteriophage vector.
D. In enzyme replacement therapy, lymphocytes from the blood of the patient are grown in a culture outside the body.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → A and B only
ADA deficiency is caused by the deletion of the gene for the enzyme adenosine deaminase, which the immune system needs. Three kinds of treatment are used: bone marrow transplantation, enzyme replacement therapy and gene therapy.
A. The enzyme adenosine deaminase is crucial for the immune system to function. — True. Without ADA the immune system cannot work properly. That is why its absence is treated as a serious disorder.
B. In enzyme replacement therapy, functional ADA is given to the patient by injection. — True. The patient receives the working enzyme directly. Like bone marrow transplantation, this approach is not completely curative.
C. A functional ADA cDNA is introduced into the patient’s cultured lymphocytes using a bacteriophage vector. — False. In gene therapy the functional ADA cDNA is carried into the lymphocytes by a retroviral vector, not a bacteriophage. Bacteriophages infect bacteria, while a retrovirus can carry the gene into human cells.
D. In enzyme replacement therapy, lymphocytes from the blood of the patient are grown in a culture outside the body. — False. Growing the patient’s lymphocytes in culture is the first step of gene therapy. In enzyme replacement therapy no cells are taken out; the enzyme itself is injected.
NCERT Extract:
Gene Therapy – “… The first clinical gene therapy was given in 1990 to a 4-year old girl with adenosine deaminase (ADA) deficiency. This 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; 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 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.”