Question:
SCID (Severe Combined Immuno Deficiency) is caused due to deficiency of which enzyme?
SCID (Severe Combined Immuno Deficiency) is caused due to deficiency of which enzyme?
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ADA-SCID is famous for being the first genetic disease treated with clinical gene therapy (in 1990 on 4-year-old Ashanti DeSilva) using a retroviral vector to introduce a functional ADA gene into her T-lymphocytes.
Updated On: Jun 19, 2026
- Adenosine deaminase
- Amylase
- Lipase
- Reverse Transcriptase
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The Correct Option is A
Solution and Explanation
Step 1: Concept
Severe Combined Immunodeficiency (SCID) is a rare genetic disorder characterized by the complete absence or non-function of T-cells and B-cells, leaving patients highly vulnerable to lethal infectious diseases.
Step 2: Metabolic Cause of SCID
Autosomal recessive SCID is primarily caused by a deficiency in the enzyme Adenosine Deaminase (ADA). - ADA is essential for purine metabolism. It catalyzes the irreversible deamination of adenosine and deoxyadenosine into inosine and deoxyinosine.
- In the absence of functional ADA, toxic dATP and deoxyadenosine substrates accumulate inside rapidly dividing lymphocytes.
- This accumulation is highly lymphotoxic, causing premature apoptosis of developing T-cells and B-cells in the thymus and bone marrow.
Step 3: Conclusion
This matches option (A). Final Answer: (A)
Severe Combined Immunodeficiency (SCID) is a rare genetic disorder characterized by the complete absence or non-function of T-cells and B-cells, leaving patients highly vulnerable to lethal infectious diseases.
Step 2: Metabolic Cause of SCID
Autosomal recessive SCID is primarily caused by a deficiency in the enzyme Adenosine Deaminase (ADA). - ADA is essential for purine metabolism. It catalyzes the irreversible deamination of adenosine and deoxyadenosine into inosine and deoxyinosine.
- In the absence of functional ADA, toxic dATP and deoxyadenosine substrates accumulate inside rapidly dividing lymphocytes.
- This accumulation is highly lymphotoxic, causing premature apoptosis of developing T-cells and B-cells in the thymus and bone marrow.
Step 3: Conclusion
This matches option (A). Final Answer: (A)
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