Given below are two statements. One is labelled Assertion (A) and the other is labelled Reason (R).

Assertion : Gene therapy was carried out for the first time to treat SCID by introducing ADA gene.

Reason : Using retroviral vector, the functional gene was delivered into patient's cells.

In light of the above statements, choose the correct answer from the options given below. 

Both ‘A’ and ‘R’ are true and ‘R’ is not the correct explanation of A.

Assertion (A) states that gene therapy was first used to treat SCID (Severe Combined Immunodeficiency) by introducing the ADA (adenosine deaminase) gene. This is true; in the early 1990s, the first successful gene therapy trials for SCID were conducted by introducing the ADA gene into patients' cells.
Reason (R) states that a retroviral vector was used to deliver the functional gene into patients' cells. This is also true; retroviral vectors were indeed utilised in early gene therapy trials to deliver the functional ADA gene into the cells of SCID patients.

The correct reason is that the adenosine deaminase is an enzyme essential for the development and function of immune cells. In individuals with ADA deficiency, the lack of this enzyme results in severe impairment of the immune system, leading to SCID. Therefore, introducing a functional ADA gene via gene therapy aims to restore the deficient enzyme activity and improve immune function in SCID patients.