The first clinical gene therapy was given for treating :

Options

A. diabetes mellitus
B. chicken pox
C. rheumatoid arthritis
D. adenosine deaminase deficiency

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks about the first clinical gene therapy and what condition it was used to treat. The options provided are diabetes mellitus, chicken pox, rheumatoid arthritis, and adenosine deaminase deficiency.

2. **Identifying the Condition Treated**: The first clinical gene therapy was conducted at the National Institute of Health in Maryland. It was administered to a four-year-old girl suffering from Severe Combined Immunodeficiency (SCID).

3. **Understanding SCID**: SCID is a disorder characterized by a deficiency in the immune system. Specifically, it is often caused by a lack of the enzyme adenosine deaminase (ADA), which is crucial for the elimination of deoxyadenosine, a toxic compound to lymphocytes.

4. **Gene Therapy Process**: During the first clinical gene therapy, a functional ADA gene was introduced ex vivo (outside the body) into the bone marrow cells of the girl. This was done using engineered retroviruses that carried the functional ADA gene.

5. **Reintroduction of Treated Cells**: After the introduction of the functional ADA gene into the bone marrow cells, these treated cells were reintroduced into the patient's bone marrow. This aimed to restore the function of the immune system by providing the necessary enzyme.

6. **Conclusion**: Based on the information gathered, the first clinical gene therapy was specifically for treating adenosine deaminase deficiency, which is linked to SCID. Therefore, the correct answer is option D: adenosine deaminase deficiency.

---