Write the function of adenosine deaminase enzyme. State the cause of ADA deficiency in humans. Mention a possible permanent cure for a ADA deficiency patient.

Explanation

### Step-by-Step Solution:

**1. Function of Adenosine Deaminase (ADA) Enzyme:**
- Adenosine deaminase (ADA) is an enzyme that catalyzes the hydrolytic deamination of adenosine and 2-deoxyadenosine.
- This process is crucial for the purine salvage pathway, which recycles purines for nucleotide synthesis.
- ADA plays a vital role in the normal functioning of the immune system by regulating the levels of toxic metabolites that can accumulate from adenosine.

**2. Cause of ADA Deficiency in Humans:**
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