Identify the correct statements for adenosine deaminase (ADA) deficiency.
(A) It is caused by the failure of synthesis of an enzyme, adenosine deaminase.
(B) It leads to inherited immunodeficiency disorder, severe combined immunodeficiency (SCID).
(C) It is attributed to a mutant ADA gene.
(D) Its treatment can be done by introducing ADA cDNA into the hepatocytes.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (A), (B) and (C) only
(A) It is caused by the failure of synthesis of an enzyme, adenosine deaminase. — Correct. Without its gene the enzyme is not made, and the immune system cannot work.
(B) It leads to inherited immunodeficiency disorder, severe combined immunodeficiency (SCID). — Correct. ADA deficiency is passed on from the parents and leaves the child with a very weak immune system.
(C) It is attributed to a mutant ADA gene. — Correct. The disorder comes from a defect in the gene for ADA, in the book’s words its deletion.
(D) Its treatment can be done by introducing ADA cDNA into the hepatocytes. — Incorrect. In gene therapy the ADA cDNA is put into lymphocytes taken from the patient’s blood, not into hepatocytes (liver cells).
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. However, as these cells are not immortal, the patient requires periodic infusion of such genetically engineered lymphocytes. However, if the gene isolate from marrow cells producing ADA is introduced into cells at early embryonic stages, it could be a permanent cure.”