Mention the cause of ADA deficiency in humans. How has genetic engineering helped patients suffering from it ?

Explanation

### Step-by-Step Solution

1. **Identify the Cause of ADA Deficiency**:
- ADA deficiency in humans is caused by a mutation in the ADA gene. This gene is responsible for producing the enzyme adenosine deaminase (ADA), which is crucial for purine metabolism.

2. **Understand the Role of Adenosine Deaminase**:
- The enzyme adenosine deaminase is involved in the breakdown of purines, which are essential components of nucleic acids (DNA and RNA). When the ADA gene is mutated, the production of this enzyme is impaired, leading to the accumulation of toxic metabolites, which can severely affect the immune system.

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