Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): In gene therapy for ADA deficiency, a functional ADA cDNA is introduced into the patient’s liver cells grown in a culture outside the body.
Reason (R): The enzyme adenosine deaminase is crucial for the immune system to function.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A) is false but (R) is true.
ADA deficiency is a hereditary disorder in which the gene for the enzyme adenosine deaminase is deleted. In the first gene therapy for it, a working copy of the gene was put into the patient’s own blood cells.
Assertion (A): In gene therapy for ADA deficiency, a functional ADA cDNA is introduced into the patient’s liver cells grown in a culture outside the body. — False. The cells used are lymphocytes from the blood of the patient, not liver cells. The lymphocytes are grown in a culture outside the body, the functional ADA cDNA is introduced into them with a retroviral vector, and they are then returned to the patient.
Reason (R): The enzyme adenosine deaminase is crucial for the immune system to function. — True. ADA is needed for the immune system to work. This is why a child who lacks it suffers from a serious immune disorder.
Since A is false and R is true, option (3) is the answer.
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. … 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.”