(a) Name the deficiency for which first clinical gene therapy was given.
(b) Mention the cause of and one cure for this deficiency.

Explanation

### Step-by-Step Solution:

**(a)** The deficiency for which the first clinical gene therapy was given is **Adenosine Deaminase (ADA) deficiency**. This therapy was administered to a four-year-old girl in 1997.

**(b)**
1. **Cause of ADA Deficiency**: The cause of this deficiency is the lack of the enzyme **adenosine deaminase**. This enzyme is crucial for the proper functioning of the immune system as it is involved in the metabolism of purines in lymphocytes.

2. **Cure for ADA Deficiency**: There are several approaches to cure ADA deficiency:
...