Question

When a patient with defective ADA was treated, which of the following steps was performed for gene therapy?
 (i) Lymphocytes were obtained from the patients.
 (ii) Lymphocytes are transferred to culture dishes.
 (iii) Lymphocytes were transfected with normal ADA genes.
 (iv) The transfected cells are returned to the patients.

A) All of the above
B) (iii) and (iv)
C) Only (iv)
D) SCID cannot be treated

Answer 1

Hint: Gene therapy is the introduction of genes into existing cells to prevent or cure a wide range of diseases. It corrects defective genes responsible for disease development. It was first used in 1990 on a girl Ashi Disilva for treatment of SCID (severe combined immune deficiency).
Complete step-by-step answer:
ADA is adenosine deaminase deficiency which is an autosomal recessive disorder causing immunodeficiency. It can be treated with gene therapy. First of all, lymphocytes are taken from the blood of the patient and are grown in a culture in vitro. After that ADA cDNA that is functional is introduced into these lymphocytes by using a retroviral vector. After that these lymphocytes are put back into the patient. This process is repeated after a regular interval of time. This can be cured permanently if the functional ADA gene is isolated from bone marrow cells and put in during the early embryonic stages.
Hence the correct answer is option A.

Note: Gene therapy can be accomplished by: 1) Replacing a mutated gene that causes disease with a healthy copy of the gene. 2) In activating or ‘knocking out a mutated gene that is functioning improperly. 3) Introducing a new gene into the body to help fight a disease.