Question

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

Answer 1

Hint: Adenosine deaminase (ADA) deficiency is a hereditary condition that affects the immune system. It makes the human body unable to respond to infections, along with symptoms like pneumonia, delayed growth, chronic illness, etc.

Complete answer:
Adenosine deaminase, basically a protein, helps in the activation of lymphocytes, a type of white blood cells which plays a vital role in immune action to infections.
1. The most important functions of adenosine deaminase enzyme are;
- It catalyzes the hydrolytic deamination of adenosine and 2-deoxyadenosine.
- It is essential for the normal function of the immune system.
- It is a vital enzyme of the purine salvage pathways.

2. Cause: This hereditary disorder is caused due to the deletion of the gene functioning for adenosine deaminase. It is an autosomal recessive disease, that is the person must have this mutation in both copies of the particular gene.

3. Treatment: ADA deficiency must be cured at the infant stage or most preferably, the foetal stage. In some instances, this can be treated either by bone marrow transplantation, or by enzyme replacement therapy. Since both of these are not completely curative, gene therapy is considered the most effective.
- In this treatment, lymphocytes from the blood of the patient are grown in an in vitro culture. After introducing a functional ADA cDNA using a retrovirus, into these lymphocytes, they are again transferred back to the patient's blood. Also, the patient requires periodic infusion of such genetically engineered lymphocytes, as these cells cannot regenerate.
- It could be a permanent cure, if a gene isolated from bone marrow cells producing ADA is introduced into the cells, at early embryonic stages.

Note: ADA deficiency is a common cause of severe combined immunodeficiency (SCID) which directly affects the function of T and B cells. The first gene therapy was given to a four-year old girl with ADA deficiency, in 1990.