Which among the following is a cause of adenosine deaminase deficiency?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Due to the deletion of the gene for adenosine deaminase.
Adenosine deaminase (ADA) is an enzyme needed for the immune system to work. A child who cannot make it has a serious immune disorder, ADA deficiency. The disorder is caused by the deletion of the gene for adenosine deaminase, so the enzyme is not made at all. It was the disorder treated by the first clinical gene therapy, in 1990, in which a working copy of the gene was supplied.
Option (1) Due to the inversion of the gene for adenosine deaminase. — Incorrect. An inversion turns a piece of a chromosome around. The book gives deletion, not inversion, as the cause of ADA deficiency.
Option (2) Due to the deletion of the gene for adenosine deaminase. — Correct. The gene for ADA is deleted, so the child has no enzyme and the immune system fails.
Option (3) Due to the gain of the gene for adenosine deaminase — Incorrect. Gaining a gene would add ADA, not remove it. A deficiency comes from losing the gene.
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.”