Which of the following statements regarding gene therapy is/are correct ?

Options

A. It is an application of biotechnology, in which a defective gene is manipulated by introduction of a normal, healthy and functional gene
B. The genetic disorders that are being investigated for gene therap, range from sickle-cell anaemia to severe combined immuno-deficiency (SCID)
C. The first clinical gene therapy was given in 1990 to a 4-year old girl with adenosine deaminase (ADA) deficiency
D. all of these

Answer

### Step-by-Step Solution:

1. **Understanding Gene Therapy**:
- Gene therapy is a medical intervention that involves the alteration of genes to treat or prevent diseases, particularly genetic disorders. It aims to replace, inactivate, or introduce genes into cells to correct genetic defects.

2. **Analyzing the First Statement**:
- The first statement claims that gene therapy involves manipulating a defective gene by introducing a normal, healthy, functional gene.
- This statement is correct because the primary goal of gene therapy is to replace or repair defective genes to restore normal function.

3. **Analyzing the Second Statement**:
- The second statement mentions that genetic disorders investigated for gene therapy include sickle cell anemia and severe combined immunodeficiency (SCID).
- This statement is also correct as both conditions are genetic disorders that can potentially be treated through gene therapy by correcting the underlying genetic defects.

4. **Analyzing the Third Statement**:
- The third statement asserts that the first clinical gene therapy was administered in 1990 to a 4-year-old girl with adenosine deaminase deficiency (ADA deficiency).
- This statement is correct as the first successful gene therapy was indeed performed on a child suffering from this condition, which is a form of SCID.

5. **Conclusion**:
- Since all three statements regarding gene therapy are correct, we can conclude that the answer is that all of the statements are true.

### Final Answer:
All of the statements regarding gene therapy are correct.

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